CADC: add routine to remove DP recipe instances
DB: remove unnecessary return from change_state
DB: extract private _change_state method

This allows the routine to be called from within an existing
database lock/cursor context.
DB: add option to change state when moving jobs

By default the job will be reset to the UNKNOWN state and an
automatically generated log message will be written.
CADC: add a routine to move jobs from CADC to JAC