main: Rename "Recent" section to "Videos"

The recent section shouldn't be called "Recent". We
chose not to show recent videos and show the user's videos instead,
along with the locally download ones, and optical media.

"Videos" is simple, and already translated. It also matches what
gnome-photos uses for its equivalent view.

https://bugzilla.gnome.org/show_bug.cgi?id=725337