Merge: Prepare Android projects to be compiled in release mode for F-Droid

This PR prepares the Android projects to be compiled in release mode by Jenkins (or a cron) for F-Droid. It adds the `android-release` rule to all Android projects and it vectorizes the fonts in the logos to get the desired result when the font is not installed.

At this point, the release APK file is written over the debug one, this should not be such a big problem as we usually use both separately.

@privat To prepare to compile in release mode on the server you can follow the instructions at the end of http://nitlanguage.org/catalog/android.html , it's pretty much a single command to generate a keystore. We'll have to find a way to manage the key to the keystore... For the TSA server, we could use http://tsa.safecreative.org/ but it's limited to 5 timestamps per days so we would need to choose our requests.

Pull-Request: #1710
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Jean Privat <jean@pryen.org>