Fixes issue #3612379.

Fixes issue #3611920, but keep the issue open because more activities
will be added.

Android doesn't currently store bundles persistently, so it's premature
to protect against accidental information leaks through persistent
bundle storage. Protecting against deliberate information leaks by the
OS is probably futile, so there's currently no need for bundle
encryption.

Fixes issue #3611925.

Fixes issue #3611959.

Only the ARM binary is included at present. Better control of the Tor
process is needed - it's possible for it to be left running when Briar
exits, and if the cookie file is deleted it's no longer possible to stop
the process.

If the group's owner is spamming, unsubscribe.

This keeps the visual language consistent: rating icon plus name equals
author.