add params to collection filter

[aka47]

To filter a collection you can define COLLECTION_FILTER and use them like "filter:".

With this PR you can also params to those filter and use them like "filter:param". The COLLECTION_FILTER will be called with the params a second argument.

This ideas was already mentioned in the initial PR for COLLECTION_FILTERS, but not implemented. (#947)

[pablobm]

Thank you for your PR @aka47 - I think it's good. Generally I'm inclined not to enhance the search, as I think it should be completely redesigned, but your change is a small increment of what we already have, so I think it's fine.

Would you be able to make the following two changes before I merge this?

1. This PR creates a situation where searching for anything with a colon in the middle (eg: "order:12") will stop working if it's intended as a string search. Before it only broke things if the colon was at the end, which I think was a much less common case. Would you be able to tweak your code to avoid this? I think you could change it so that filter? not only does the regexp match, but also sees if the filter name exists in COLLECTION_FILTERS. Does that make sense?
2. Fix that Hound warning (or any other that may come later).

[aka47]

@pablobm thanks for your feedback - sure filters and terms should not get confused. It needed a bit more changes then I thought, as the Query class does not have access to the Search Class and the valid_filters from the dashboard.
If you need anything more - please tell me.

[mmrobins]

FWIW this is great and I would love to see it released. I was running a hacky version of this in my local code to do the same. I get that search needs an overhaul, but until then something small like this would be a great incremental improvement in the meantime.

[pablobm]

Thank you @aka47!