Application menu should fall back to set application name

The app menu tries to find the application name from its associated desktop file. If that isn't present, it just shows 'Unknown Application Name' in the app menu. I'd like to suggest some changes here:

 - Use a shorter string for the fallback. "Unknown Application Name" is insanely long and doesn't help. If the fallback label was just "Application" it would look pretty much fine. In fact, it would avoid the name repetition that you get when anything sets an application menu.

 - Try to fallback to the application name set as WM_NAME instead of using the unknown string for the application menu label.

 - Also set the application name (I don't know what it's called... the unclickable indicator in the top left ) to WM_NAME, rather than falling back to the window title.