The method used by Commons IO to get the available disk space fails on
Android devices that lack a df binary - use the Android API instead.

This removes the other projects' dependency on the Android API.

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.

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.

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.

Guice only requires javax.inject.jar at runtime.

This should make it possible to develop the core in Eclipse without the ADT.