We should have a way to say "show me all release groups that are either EP or Single".

Once the code for work filtering is merged, the same should apply to work types.

For RG secondary types, we should be able to choose whether we want to select an AND or OR combination - "show me any RGs which are either Soundtrack or Compilation" or "show me any RGs which are both Soundtrack and Compilation". I assume this would be easiest to do with an additional checkbox.