MainWindow code

All back buttons are implemented
.
Merge remote-tracking branch 'origin/master'

Conflicts:
	Tetris/bin/Debug/Tetris.exe
	Tetris/bin/Debug/Tetris.pdb
	Tetris/obj/Debug/DesignTimeResolveAssemblyReferencesInput.cache
	Tetris/obj/Debug/Tetris.csproj.GenerateResource.Cache
	Tetris/obj/Debug/Tetris.exe
	Tetris/obj/Debug/Tetris.pdb
	Tetris/obj/Debug/Tetris_MarkupCompile.cache
	Tetris/obj/Debug/Tetris_MarkupCompile.lref