Add Transifex config
Override _responsive_topnav for translations

https://github.com/mysociety/alaveteli/issues/2033 causes overridden
translations to be obsoleted by gettext:find_theme.

Overriding the template puts the msgids in to the templates find_theme
is searching, so they are used correctly.
Generate theme translations

- Remove en as primary locale is en_UG and provided by alaveteli core
- Add fr
Merge branch '27-theme-translations'