implement StaticRouting Layer

[amdfxlucas]

Replacement for BIRD ( RoutingLayer) that manually sets up 'ip route's on the nodes without any routing daemon.
For straightforward topologies i.e. border-routers and hosts on the same local net ("net0") dynamic routing is overkill (unneccessary expense of CPU ) and can be replaced by static routing.
This however does not hold for vast internal AS topologies.

[amdfxlucas]

This represents the more general approach to achieve what #30 does attain within SCION AS scope. StaticRouting with linux kernel means only instead of BIRD routing daemon. This PR is not obsolete since SCION ASes with an internal topology more intricate than 'all BRs and hosts in the same local net' still require dynamic routing in the absence of a StaticRouting layer which would compute the required iptables rules at build time.