expanded Client_data to hold two addresses (IPv4, IPv6) instead of one

Compilerflag: CLIENT_ONETOONE_IP (to define in DHT.h, default unset i.e. NEW case: two addresses)

Every function in DHT{_test}.c working on Client_data has been rewritten to store IPv4 addresses in assoc4, IPv6 addresses in assoc6.
Loading/Storing of states defined with either compiler switch on or off is transparently adjusting to the differences.

DHT.h, DHT.c:
- introduction and handling of the structure changes

DHT_test.c, Messenger.c:
- logging adapted to new structures

util.h:
- LOGGING isn't undefined per default anymore