Updating OpenFace to version 2.2.0 (#741)

Change log:

Moving to C++17. This means that the code can only be build using C++17 compilers (e.g. g++ >8 and Visual Studio 2017, clang > 5), fixing related bugs - (#698, #629, #641)
Removing an explicit dependency on boost (all the filesystem operations are performed using std::filesystem or boost::filesysteme). If boost is available it will used boost:filesystem, otherwise std::filesystem (this requires C++17)
Visual Studio 2017 is now the main version for Visual Studio builds, VS 2015 is no longer supported
Updating OpenCV to 4.1 version (#511)
Fixing a bug with output images when using GUI (#694)
Updating RAWImage - #609, so it can be initialized from System.Drawing.Bitmap directly
Fixing overlap detection for multi face tracking (#693)

lib/3rdParty/OpenCV/include/opencv2/gapi/util/optional.hpp

@@ -0,0 +1,178 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+//
+// Copyright (C) 2018 Intel Corporation
+
+
+#ifndef OPENCV_GAPI_UTIL_OPTIONAL_HPP
+#define OPENCV_GAPI_UTIL_OPTIONAL_HPP
+
+#include "opencv2/gapi/util/variant.hpp"
+
+// A poor man's `optional` implementation, incompletely modeled against C++17 spec.
+namespace cv
+{
+namespace util
+{
+    class bad_optional_access: public std::exception
+    {
+    public:
+        virtual const char *what() const noexcept override
+        {
+            return "Bad optional access";
+        }
+    };
+
+    // TODO: nullopt_t
+
+    // Interface ///////////////////////////////////////////////////////////////
+    template<typename T> class optional
+    {
+    public:
+        // Constructors
+        // NB.: there were issues with Clang 3.8 when =default() was used
+        // instead {}
+        optional() {};
+        optional(const optional&) = default;
+        explicit optional(T &&value) noexcept;
+        explicit optional(const T &value) noexcept;
+        optional(optional &&) noexcept;
+        // TODO: optional(nullopt_t) noexcept;
+        // TODO: optional(const optional<U> &)
+        // TODO: optional(optional<U> &&)
+        // TODO: optional(Args&&...)
+        // TODO: optional(initializer_list<U>)
+        // TODO: optional(U&& value);
+
+        // Assignment
+        optional& operator=(const optional& rhs) = default;
+        optional& operator=(optional&& rhs);
+
+        // Observers
+        T* operator-> ();
+        const T* operator-> () const;
+        T& operator* ();
+        const T& operator* () const;
+        // TODO: && versions
+
+        operator bool() const noexcept;
+        bool has_value() const noexcept;
+
+        T& value();
+        const T& value() const;
+        // TODO: && versions
+
+        template<class U>
+        T value_or(U &&default_value) const;
+
+        void swap(optional &other) noexcept;
+        void reset() noexcept;
+        // TODO: emplace
+
+        // TODO: operator==, !=, <, <=, >, >=
+
+    private:
+        struct nothing {};
+        util::variant<nothing, T> m_holder;
+    };
+
+    template<class T>
+    optional<typename std::decay<T>::type> make_optional(T&& value);
+
+    // TODO: Args... and initializer_list versions
+
+    // Implementation //////////////////////////////////////////////////////////
+    template<class T> optional<T>::optional(T &&v) noexcept
+        : m_holder(v)
+    {
+    }
+
+    template<class T> optional<T>::optional(const T &v) noexcept
+        : m_holder(v)
+    {
+    }
+
+    template<class T> optional<T>::optional(optional&& rhs) noexcept
+        : m_holder(std::move(rhs.m_holder))
+    {
+        rhs.reset();
+    }
+
+    template<class T> optional<T>& optional<T>::operator=(optional&& rhs)
+    {
+        m_holder = std::move(rhs.m_holder);
+        rhs.reset();
+        return *this;
+    }
+
+    template<class T> T* optional<T>::operator-> ()
+    {
+        return & *(*this);
+    }
+
+    template<class T> const T* optional<T>::operator-> () const
+    {
+        return & *(*this);
+    }
+
+    template<class T> T& optional<T>::operator* ()
+    {
+        return this->value();
+    }
+
+    template<class T> const T& optional<T>::operator* () const
+    {
+        return this->value();
+    }
+
+    template<class T> optional<T>::operator bool() const noexcept
+    {
+        return this->has_value();
+    }
+
+    template<class T> bool optional<T>::has_value() const noexcept
+    {
+        return util::holds_alternative<T>(m_holder);
+    }
+
+    template<class T> T& optional<T>::value()
+    {
+        if (!this->has_value())
+            throw_error(bad_optional_access());
+        return util::get<T>(m_holder);
+    }
+
+    template<class T> const T& optional<T>::value() const
+    {
+        if (!this->has_value())
+            throw_error(bad_optional_access());
+        return util::get<T>(m_holder);
+    }
+
+    template<class T>
+    template<class U> T optional<T>::value_or(U &&default_value) const
+    {
+        return (this->has_value() ? this->value() : T(default_value));
+    }
+
+    template<class T> void optional<T>::swap(optional<T> &other) noexcept
+    {
+        m_holder.swap(other.m_holder);
+    }
+
+    template<class T> void optional<T>::reset() noexcept
+    {
+        if (this->has_value())
+            m_holder = nothing{};
+    }
+
+    template<class T>
+    optional<typename std::decay<T>::type> make_optional(T&& value)
+    {
+        return optional<typename std::decay<T>::type>(std::forward<T>(value));
+    }
+} // namespace util
+} // namespace cv
+
+#endif // OPENCV_GAPI_UTIL_OPTIONAL_HPP