Filter options and work item type compatibility

Now that all kinds of different work items are visible together in various planning views, it's possible that filter combinations are not compatible with certain work item types.

For example if you select to filter by 'color' and 'type', you should only see options for 'type' (work item type) which can have a 'color' value.

Likewise, if you select a 'type' filter of 'Epic', you shouldn't be able to add additional filters which are not compatible with epics (e.g. 'iteration' should not be a filterable option).

This change should apply to all places where it's possible to filter by different work item types.