Adds a new `Info` method to the Kademlia endpoint that returns the following local node info:
* ID
* Type
* Metadata (email and wallet)
* Restrictions (free storage and bandwidth)
The new endpoint is exposed as `inspector kad node-info` command too.
We realized that the Kademlia FindNear() function was
1. not using XOR distance (AKA _totally broken_)
2. largely a duplicate of the RoutingTable FindNear() function
Changes in this PR:
1. upgraded RoutingTable FindNear() to use iterator and restrictions
2. removed unneeded RoutingTable interface
3. made Kademlia wrap methods that were previously accessed via RoutingTable
4. fixed the tests
now kad inspector features exist on every server that has
kademlia running. likewise, overlay and statdb.
this means kad inspection features are now available on
storage nodes
Change-Id: I343c873552341de13302bfb7a5d79cccc84fc6b8
