Adds multi-hosting service to Neo4j Server.

 o Adds a configuration database to the Server, containing
   meta data about hosted databases.
 o Adds database registry, managing live hosted databases.
 o Adds runtime reconfiguration of databases - dropping, creating,
   changing config and mode.
 o Contains several provisions ensuring full backwards compatibility
   with previous 'db' database and it's associated configuration.
   If a legacy config file exists, it overrides hosted config.
 o This commit *only* contains these new services, they are not
   plugged in. This is meant to incorporate this piece-meal by
   first moving the new code in, and plugging it in in a follow-up
   commit.

Conflicts:
	enterprise/com/src/test/java/org/neo4j/com/ServerTest.java