Internationalise JavaScript code

I don't want to leave TODOs everywhere

Reference:

• https://docs.djangoproject.com/en/1.8/topics/i18n/translation/#internationalization-in-javascript-code

added dev label

Should also be done with this: https://gitlab.com/fdroid/repomaker/merge_requests/77#note_31763834

mentioned in issue #110 (closed)

added Doing and removed ~2112488 labels

closed via merge request !113 (merged)

Reopening due to !119 (merged).

reopened

closed via merge request !120 (merged)

removed Doing label