Some devices don't support IPv6, so we'll need to bind separate IPv4 and
IPv6 sockets and advertise both addresses.

(Although it isn't possible to create an identity yet...)

The invitation and private messaging UIs are currently broken. Some key
rotation bugs were fixed; others may have been created (unit tests
needed). An encoding for private keys was added. Pseudonyms were moved
out of the messaging package and ratings were moved in.

The Tor plugin tests are consistently failing with the latest versions
of Silvertunnel and Spongy Castle; we may need to ship native Tor
binaries for Windows/Mac/Linux and use Orbot on Android.

The UI may access the DB in response to UI or DB events; to maintain a
consistent view of the DB's contents, the tasks performing these
accesses must be prevented from overlapping, and must produce consistent
results if reordered. A single-threaded executor and latches are used to
prevent tasks from overlapping, without blocking non-UI access to the
DB.