Added filter mechanism to combined search.

[demiankatz]

• Now you can provide multiple views into a single search backend.

[EreMaijala]

Yay!

[demiankatz]

Does this actually meet a use case for you, or are its limitations (namely, the fact that it doesn't easily translate into the tabbed search box) a significant problem? I'm trying to decide whether this is useful to commit as-is, or if deeper functionality needs to be implemented to make it richer. (Though if deeper functionality is needed, I have no brilliant ideas on how to do it cleanly).

[EreMaijala]

We're not using a tabbed search box, only results, so that's not a limitation for us.

[demiankatz]

Excellent. In that case, I'll definitely merge this sooner or later, but I'll probably leave the PR open for a couple of weeks in case I have any new ideas to expand/improve it (perhaps from brainstorming at the Summit). If you have any suggestions regarding configuration or code, they'd definitely be welcomed!

[demiankatz]

I've gone ahead and merged this to master. There's still room for better mechanisms elsewhere in VuFind, but this seems like a reasonable enhancement for CombinedController as it is.