Rewrite and simplify name_list a bit.

Rework name_list, removing unnecessary variables and cleaning up the
code.  It also doesn't load full transactions from disk anymore, since
they are already in the wallet.  It has to access the txindex, though.
Further tweak name_list.

Load also the txindex from disk only right before it is actually used.
This skips the disk access entirely if we don't have a name tx at hand.
Merge pull request #61 from domob1812/name-list

Name list improvements