And potentially optimize.

Currently every 'update build' event in buildbucket results in running a datastore query on Console.

However:
  * Consoles change very infrequently
  * Console definitions are updated in a single place (by UpdateConsoles)
  * Console's are scoped to a single project

I'm thinking:

  * Have a Consoles(project) root entity with the list of all consoles
  * Have a Consoles(project) <- ForBuilder(builder) entity with the list of consoles
    for a given builder
  * Have UpdateConsoles transactionally update the Consoles and ForConsoles objects
  * Do direct Get operations on the relevant entities (no query), and rely on dscache to cache their access in memcache.