Initial version where search engines are stored per search, not per file.
The list of enabled engines is stored with the parameter set.

QuaMeter group goes into Reporting.
Missed switch branches for allowed values.
Validation only uses enabled search engines.
Named foreign keys so they can be referenced later.
All other foreign keys are named.
Working towards moving the enabled_engines to be referenced by search_parameters.
Removing explict names for foreign keys. The DDL script takes care of that.
Introduced EqualityCriteria that makes the modifications of the classes much easier.
Migration complete together with search parameters taking over enabled_engines.
Forgotten key rename.
Enabled engines need to get copied around.
Nothing enabled by default...
Fixing tests.
Quameter SQL needed to be updated.
Enabled engines get selected properly.
Get rid of last nulls in enabled_engines for search_parameters with no associated actual searches.