IPv4/IPv6: dynamic registration of upper layer protocols; merge IPv?NetworkLayer's transport gates

TCP, UDP, SCTP, RSVP, OSPF, MANET are all merged into transport gates.
Network user modules must register their protocol number by sending
an IPRegisterProtocolCommand from initialize.

Introduced an IPSocket class that wraps the registration process.
FWMath.h: TraCIMobility didn't compile with MSVC
Added Ieee80211 carrier sense tests.

Covers mutual transmissions for in range and out of range,
synchronized and delayed scenarios.
Added a new IPv4 route check.
BIG REFACTORING -- TODO split up commit; describe changes in commit message
ARP: refactoring: ARP is now next to the IPv4 module not below it; see TODO below!

Motivation:
 - performance improvement (datagrams no longer go through ARP)
 - conceptually better (packets to PPP no longer flow through ARP)
 - more consistent with how IPv6 and NeighbourDiscovery are organized

TODO:
 - update NED docu of both ARP and IPv4!
 - proxyARP is now both in IPv4 and ARP??
 - refactor ARP gates: queueIn+ipIn/queueOut (all connecting to IPv4 though)
 - note: IPv4RoutingDecision is now only effectively used on the ip-->arp connection
added GenericNetworkProtocol & co.
added MultiNetworkLayer
added DYMO protocol
added GPSR protocol
added RIP protocol