Visual Studio Builds: Link to libepoxy

Patches have been submitted to the libepoxy project so that it can be built
under Visual Studio.  This will allow the GDK, GTK and gtk3-demo projects
to build, but the gtkglarea code is not usable at this time as
implementation needs to be added to the GDK-Win32 backend for it.
Visual Studio Builds: Update the gtk3-demo Projects

The gtkglarea and sidebar demos have been added, so build them in the
projects.  Note that the gtkglarea code is not usable under Windows at this
point as implementation is needed for the GDK-Win32 backend.
Visual Studio Builds: Update "Installation"

Add the newly-added public headers for GDK and GTK into the list of files
to "install".
Updated Serbian translation