added network statistics to jool.
minor changes to ip_statistics
First revision of issue #41.
There's still some stuff to take care of, but I wanna merge first.
Merge branch 'ip_statistics' into issue108

Conflicts:
	mod/compute_outgoing_tuple.c
	mod/core.c
	mod/packet.c
	mod/translate_packet.c
	mod/ttp/4to6.c
	mod/ttp/6to4.c

Lots of TODOs remain.