Migrate to txdbus

[micolous]

Presently, tollgate uses dbus-python in order to talk over DBus. This has some major problems:

• It requires that a binary module be compiled
• It can't run inside of a virtualenv
• It uses autotools rather than distutils for packaging, meaning pip can't install it.
• It doesn't appear to be actively maintained.

A lot of this centres around this bug.

There's another implementation of DBus, written in Python (without a native library), called txdbus. This is written using Twisted.

This would require that the existing dbus code be ported to Twisted. This also has the bonus of being able to use Twisted's daemonisation instead of daemonize which can refer to about three different distinct packages with the same egg name.

[micolous]

I've ported micolous/cbus to txdbus in a branch, and it seems to work well. Some gotchas:

• All of the methods use Twisted Deferred objects, which requires some wrapping around (defer.inlineCallbacks), but this prevents the methods from returning a value.
• Subjective examinations show that txdbus is much faster than python-dbus.
• Tollgate's backend daemon will need to be ported to twisted (but this is probably good as it means it could maybe run in twistd)

Need to keep these in mind when porting tollgate.