Fixed SIP and PJSIP logging

Ignore-this: 938803e8ae3b3620d79a3758cdd3fa97

Don't log by default, expose settings for toggling SIP and PJSIP
logging respectively.

darcs-hash:20130918143950-56b4d-9af60797f3877259358a0b7bd5b22dcf97d7f15b
Removed no longer needed code

Ignore-this: 7138903c3affd1d7c1ea83334d22c4c9

Device fallback is now taken care of by the engine.

darcs-hash:20130918144745-56b4d-73da7a94533ef9a51d906cc8e1d2ab03185ae080