Networker reordering; remove / change dependencies

  - move serv_network.h into modules/network where it belongs...
  - move structs out of serv_network.h into their respective headers
  - serv_expire doesn't need serv_network.h anymore, it seems to get the usetable struct from elsewhere
  - the netfilter module was moved to the network directory, it seems to be closely dangled to networking
  - move all code about the netfilter (config reading) into serv_netfilter.c
  - move the code networker related from msgbase.c:CtdlDoIHavePermissionToPostInThisRoom() into serv_netconfig.c:netconfig_check_roomaccess()
  - move the filterlist instance into serv_netfilter.c

lesson learned the hard way today: if you move a header, flush the dependencies, else the make process will abort with no usefull message at all.
 -> Gentlemen please flush the dependencies and rebootstrap your workingcopy.