[mod] manage - implement babel commands, drop update_translations.sh

In ./manage implement babel.*:

-  extract   : extract messages from source files and generate POT file
-  update    : update existing message catalogs from POT file
-  compile   : compile translation catalogs into binary MO files

Replace searx_extra/update/update_translations.sh by command:

- ci.babel.update

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>