Add "implied VRF" to pool list/search

This includes the "implied VRF" when listing and searching for pools. A
pool is only allowed to have member prefixes in one VRF and so we can
derive which VRF that is by looking at one of the prefixes that is
currently a member of the pool.

Part of #291
Fixy fixy
CLI now lists the implied VRF of a pool

And a small bug fix so that the prefixes of the pool are actually
included in the output ;)

Part of #291
Add default variable to pool for VRF

Part of #291
Add implied VRF to pool in CLI listing

It is now possible to search and list the implied VRF through the CLI
client. This required a few other changes and I took the chance to
rewrite the pool listing to use a smart search instead of the old lame
way.

I really just did the CLI to test. The issue only involved fixing the
backend and possibly pynipap... hmm, this leaves jnipap, right? No one
likes Java anyway.

Fixes #291