widgets: fix msgmerge warnings

Just to make msgmerge happy, though.
It would also slightly make the strings translator-friendly.
I'm not familiar with Python so it may require some review and
codingstyle tune.
Signed-off-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Merge pull request #270 from Vdragon/fix_gettext_warning

widgets: fix msgmerge warnings

Signed-off-by: David Aguilar <davvid@gmail.com>