* Launch apps by their full desktop file name
gtk-launch only appends the .desktop suffix when the argument doesn't
already end with it. Apps whose desktop id itself ends in .desktop --
notably Telegram (org.telegram.desktop.desktop) -- were therefore looked
up as a nonexistent file and silently failed to launch from the menu,
while every other app worked.
Passing the full file name to gtk-launch resolves the entry
unambiguously for both naming styles.
* Clarify launch comment wording
