Unique index removed from unused ISSearch database table

The unique index IX_ISSearchSourceTypeSource on the ISSearch has been removed and replaced with a non-unique index.

A special "App\Db.ISSearch" entry has been written to the Registry table to identify this since it is a mid-cycle database change.

This model database finPOWERConnect.is has also had these changes applied so any new database will be correct.

NOTE: This table is not currently used.