Merge branch 'build-FPE-update-zip' into 'master'

Build Privileged Extension OTA update.zip using `fdroid build`

This allows `fdroid build` to build the OTA update ZIP file for F-Droid Privileged Extension, so that the official releases can be built and distributed via the normal F-Droid channels.   This is related to #233

Ultimately the client will also have to be updated to allow it to handle the non-APK files.

See merge request !181