[GS] Added option to toggle between editor windows by "Window" menu and shortcut Ctrl+Tab (Ctrl+Shift+Tab)
Closing the main window by 'X' checks to see if the mail editor window, save
Merge branch 'master' of https://github.com/InvictusInnovations/keyhotee

Conflicts:
	KeyhoteeMainWindow.cpp
	Mail/maileditorwindow.cpp
[GS] Added new files to CMakeLists.txt