Minor formatting
Mask and keep lower bits after APCI in A_Restart-PDU

This enables us to handle master resets, and check on bits that are 
required to be 0.
Comment out test case for resetAddress, conflicts with other tests
Use KNX test devices from Util, improve tests of authorize response
Reset sequence counters on disconnect

On server-side, we skip transition to state CONNECTING which resets 
the counters, but directly go to OPEN_IDLE. In the case of a re-connect, 
the previous disconnect has to reset the counters.
Add partial implementation of keep-alive to not disconnect on timeout
Destroy correct destination before creating it again
Minor formatting
Revise toString to better address the different connection modes