I18n: Update translation ast (99%).

218 translated messages, 2 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation sr (100%).

220 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
Add a space between icons to fill the entire screen.

Signed-off-by: Eric Koegel <eric.koegel@gmail.com>