Merge branch 'temp-button-action' into upstrem-button-action

[FIX] Temporary workaround for HandlerContext error.

[FIX] File size validation

[NEW] Permission list

[NEW] Adds the admin panel.

[IMPROVEMENT] immediately try to reconnect when coming from the Background.

[FEATURE] Implement FOSS build flavour

[NEW] Upload/reset avatar.

Allow giving the path to the SDK_DIR via commandline.
This makes it easier to build the project when having a custom directory
structure like fdroid's srclibs infrastructure.

Provide two build flavours 'Foss' and 'Play', the 'Play' flavour is
unchanged to what we had before. The 'Foss' flavour removes the
dependence on proprietary libraries.

This removes crashlytics, instead logging to the local log.

It also removes firebase/gcm messaging, disabling push functionality.
For now there is no replacement for this.

[CHORE] Update dependencies