Various thread safety fixes, saner use of exceptions, and code
reformatting. The Tor plugin now creates a single control connection at
startup and closes it at shutdown. Fixes issue #3611962.

See issue #3612607.

Both sides now close the connection after exchanging confirmation
results unless both results are positive.

Some Android devices require a lock to be held while using multicast, to
disable the packet filter that normally filters out multicast packets.

Fixes issue #3611924.

Partially addresses issue #3611924.

Fixes issue #3612299.

Fixes issue #3612607.

To fix issue #3611966, KeyManagerImpl's handling of TransportAddedEvent
was made asynchronous. This made it possible for a thread to call
KeyManager.endpointAdded() before the KeyManager had asynchronously
handled the TransportAddedEvent from a previous call to
DatabaseComponent.addTransport().

CryptoExecutor and DatabaseExecutor now use bounded thread pools with
unbounded queues, since running too many tasks in parallel is likely to
harm performance; IncomingConnectionExecutor, PluginExecutor and
ReliabilityExecutor use unbounded thread pools with direct handoff,
since their tasks may run indefinitely. There are no longer any bounded
executors, and all executors discard tasks when shutting down, which
fixes issue #3612189.

Responsibility for starting and stopping services has been moved from
BriarService in briar-android to LifecycleManagerImpl in briar-core.
However, BriarService is still responsible for stopping the
Android-specific executors, which is ugly. It would be better if
executors registered themselves with LifecycleManager.

Fixes issue #3611923.

Also, turn on Bluetooth if necessary before polling. Fixes issue
#3611935

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.