Collect and store static routes

[Morten Brekkevold]

In the pre-ipdevpoll era (before NAV 3.6), there existed a getDeviceData plugin to collect static routes and store their prefixes in NAV.

This plugin would cause some routers to become overloaded, as discovering static routes entails dumping the entire routing table - which isn't necessarily very optimally implemented in SNMP agents. It was therefore dropped when ipdevpoll was written as the getDeviceData replacement.

NTNU has asked us to write such a plugin again. The staticroutes plugin will be an opt-in plugin, to avoid unnecessary router load, and it will have options to throttle SNMP requests, in an attempt to reduce router load when used.