Merge branch 'remove-jars' into 'master'

Remove upstream jar files from all modules except briar-desktop

This also adds a script for running tests without the Android SDK installed

I've tried to find a better way to do this by conditionally including
the briar-android project in settings.gradle, but failed.
Please note that gradle needs to be installed to run the tests by
executing:
```
./run-tests-without-android.sh
```

See merge request !59