Consolidate Connection classes for local and remote devices

[pichler]

Currently, there are two Connection classes for connections to local and remote devices with different functionality. By consolidating the two classes, common usage of connections (independent from the used connection) should be ensured.

Future behaviour to be discussed:

• Device scan should also return local devices, if they provide BACnet objects
• Connect to a local device has no effect because they are already "connected"
• Scan for channels should work (having in mind, that scanning for other properties than Present Value should be possible in future)