Asterisk Realtime backend

See: feature request #629

Not implemented currently, but there is no reason why it can't be.

FreePBX will not support directly editing the realtime database -- this is silly. While you are changing things, the PBX is likely to be in a 'broken' state (ie, you might have incoming calls that go nowhere; IVRs that loop; dogs and cats, living together.. mass hysteria!).

asterisk-realtime should just be another ConfigBackend, like writing to the .conf files.