Replace TreeRoutingTable with OptimizedTreeRoutingTable.

* Update docstrings.
* Drop setting of `failedRPC` attribute in contacts.
* Groom code style a bit.
* Update tests.
added placeholder for notary and arbitrator-tables if they are empty.
Fix typos in /docs/markets
968 - Continuing on failed apt-get update
Merge pull request #1093 from fanquake/docs_typo

Fix typos in /docs/markets
Merge pull request #1092 from davalb/empty-notaries

added placeholder for notary and arbitrator-tables if they are empty.
Merge pull request #1067 from Renelvon/drop_tree_routingtable

Drop TreeRoutingTable