gb3android v0.3.1

• Each gb2c server now has a tribune picker in Settings: open Tribunes (x/y) and check the tribunes to display. All and None shortcuts are provided.
• All discovered tribunes are still shown by default, so existing setups keep working.
• The previous single-server tribune selection is migrated automatically.
• Saving a new selection updates the tribune bar, removes posts from deselected tribunes and restarts the affected streams.
• The app metadata is now version 0.3.1 (versionCode 7).