feat(prejoin): Add precall connection quality indicator

* Adds a dropdown indicator which displays the status of the internet connection.
* It uses the same data as `https://network.callstats.io`.
* The algorithm for the strings displayed to the user is also the one used on `network.callstas.io`.

css/main.scss

@@ -102,5 +102,6 @@ $flagsImagePath: "../images/";
 @import 'premeeting-screens';
 @import 'e2ee';
 @import 'responsive';
+@import 'connection-status';
 
 /* Modules END */