Add 'mandatory' flags to Parameter Selectors

[nielsdejong]

Both as a visual help and in the use of Forms, it it important that some parameters should be filled in mandatorily.
For a form, the submit button should not work if any of the selected items had the 'mandatory' flag, and the parameter box should get a red outline. For regular parameter reports, mandatory-ness is just a visual cue to the users.

[michela]

Thanks. In our use case atm it's possible to have a query fail or not submit properly without any user notification if a field with autocompletion does not have a correct value selected - e.g. left blank OR text entered but then autocompletion result not selected