Allow filtering on modifier values

[gnarula]

This in conjunction with thehyve/transmart-core#481 adds a feature to filter on modifier values for a particular concept. The different modifier values would be ORed together in the constraint.

For an example, consider Demo Concept, which might be modified by Compound Names. The feature allows filtering on a subset of Compound Names as demonstrated in the example below:

Option to apply modifier constraint

Option to select and filter constraints and their values