(WIP!) Replace bluez layer

* Increase abstraction by using different method names than the dbus interface (at least underscore instead of camel case)
* Add alternative implementations for BlueZ versions 4 and 5
Fix bugs in bluez 5 layer
Fix AuthAgent
Fix Networking plugin for BlueZ 5
Implement Adapter.create_paired_device
add missing kwargs parameter to signal handler function
Fix create_paired_device for bluez5
Fix BlueZ 5 handler wrapper in PropertiesBlueZInterface
Reformat blueman/plugins/applet/SerialManager.py
Replace direct signal receiver calls concerning BlueZ Device and Adapter interfaces
Reformat blueman/plugins/applet/Headset.py
Fix unhandling PropertyChanged signal for BlueZ 5
Reformat blueman/plugins/applet/PulseAudio.py
Reformat blueman/plugins/applet/NMPANSupport.py
Replace immediate references to BlueZ (4) interfaces
Fix Headset signal AnswerRequested
Stop discovery after timeout

Seems like BlueZ 4 set Discovering to 0 itself after 10.24 secs, but BlueZ 5 does not
Fix Adapter.CreatePairedDevice (BlueZ 5)
Remove agent method ConfirmModeChange

It's both deprecated and unused
Add agent metho AuthorizeService

New name for Authorize; we just define an alias to maintain backwards compatibility