Updated Latvian translation
Update Arabic translation
Port the terminal launching to GAppInfo

... dropping the use of eel-gnome-extensions and libgnome-desktop.

This fixes the build with libgnome-desktop 3.7.90 where the terminal
launching functionality was dropped. Instead, we use GAppInfo with the
G_APP_INFO_CREATE_NEEDS_TERMINAL flag as a replacement.
Release 0.20
Post-release version bump to 0.21
Finnish translation update by Jiri Grönroos
Updated Malayalam Translation
Updated LINGUAS