ENH: Adding Association Constriant to qtAttributeView
- Added the ability to indicate that all persistent objects that can be associated to a particular type of attribute must be.
- Refactored qtAssociationWdiget into an abstract class and a concrete implementation called qtAssociation2ColumnWidget - this should allow for easier customization
- Added the ability to customize the following aspects of qtAssociation2ColumnWidget
- Title Label
- Current Column Label
- Available Column Label
- Added allAssociationMode to qtAssociation2ColumnWidget to indicate that all relevant persistent objects must be associated to a type of attribute else display the warning icon
- Removed all the old Property Mode code from qtAttributeView
- qtAttributeView and qtAssociatioView now have virtual methods to create their associationn widgets that can get overridden - in the future they should use a widget factor to fetch it so you wouldn't have to create a new class to use a different association widget
Closes #343 (closed)