Implement name_pending RPC call.

Add a new RPC call "name_pending" that lists all pending name operations
in the memory pool together with some decoded information (operation
performed and value the name is set to).
Add getchains RPC command.

Implement a new "getchains" RPC command, that returns all heads of
blockchain forks known.
Add branch info to getchains.

Add additional result fields to getchains output that show the branches
connecting the heads to the main chain.
Use best height in DecodeNameTx.
Update changelog.md
Add missing STL headers.
Merge pull request #2 from phelixbtc/patch-6

Update changelog.md
Merge pull request #79 from domob1812/new-commands

name_pending and getchains RPC commands