DuplexOutgoingSession flushes its output stream if it's idle for a
transport-defined interval, causing an empty frame to be sent. The TCP
and Tor plugins use a socket timeout equal to twice the idle interval to
detect dead connections.

See bugs #27, #46 and #60.

We don't need two separate executors for long-running IO threads.

This may have been the cause of bug #69. Removed the wait-for-shutdown
code in DroidtoothPlugin that was added to attempt to avoid that bug.

This may have been the cause of Bluetooth not always being disabled at
shutdown on the Sony Xperia Tipo.

This should enable us to connect to contacts faster at startup and
whenever a new means of connecting becomes available.

The variable now wasn't being updated when no devices were discovered.

Dev task #80.

Very important stuff.

There's currently no way to set this setting, so the bug isn't fixed.