NetDB: Enforce no RIs in subdbs (Gitlab #465)

And fix FloodfillVerifyStoreJob that was looking for them there.
Fix other places that assumed RIs would be there.

- Throw IAE if attempting to store/publish RI to subdb
- Log warnings if attempting to lookup RI in subdb
- Revert changes to createPeerSelector()
- Revert peer selector changes in SearchJob and StoreJob
- Use common PeerSelector and KBucketSet for all dbs
- Revert/fix FloodfillVerifyStoreJob to looukp RIs in the main DB
- Revert "mismatch" logging in FVSJ selector, this is normal
- FVSJ log tweaks
- Don't start ExpireRoutersJob in subdbs
- Revert change in InboundMessageDistributor that was looking up RI in subdb
- Remove KNDF.isMainDb(), replace with !isClientDb()