release on F-Droid

[noerw]

The required steps are outlined here.

The simplest way to let F-Droid build Cordova apps is to include the generated Android project (platforms/android) in the source tree. We should do this through a Travis deploy step, force pushing to a separate fdroid branch (to avoid blowing up the repository size too much).

• [x] include source in git repo on branch fdroid
• [x] submit a build file to fdroiddata repo: https://gitlab.com/fdroid/fdroiddata/merge_requests/4677
• [ ] add i18n app description & screenshots (using fastlane?)
• [x] add badges to readme once merged:

[noerw]

The app now is submitted on fdroid and should be available there within the next day.

The FDroid maintainers switched to build the app from source, so the there is no need to deploy the Cordova build on a separate branch anymore.