Adjust MultiMUC support so that it stores database info about non-default MUC implementations.  This assigns a service ID, necessary for various functions/mappings, and should make for a cleaner implementation.
Also tweaked the way columns are added for SQL Server and Oracle in update 17, based off some reading on proper ALTER TABLE calls.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@10101 b35dd754-fafc-0310-a699-88a17e54d16e