ESLint

Enable ESLint on jitsi-meet with the same configuration and the same
goals as in lib-jitsi-meet.

.eslintignore

@@ -0,0 +1,11 @@
+# The build artifacts of the jitsi-meet project.
+build/*
+
+# Third-party source code which we (1) do not want to modify or (2) try to
+# modify as little as possible.
+libs/*
+
+# ESLint will by default ignore its own configuration file. However, there does
+# not seem to be a reason why we will want to risk being inconsistent with our
+# remaining JavaScript source code.
+!.eslintrc.js