integration with fieldcollapsing

[djay]

https://github.com/collective/collective.fieldcollapsing is a related plugin which lets you search items but group (and merge the results) based on different criteria. It works independent of collection filter and it works will collectionfilter ok except a few minor thing

• it would be nicer for the user is merging automatically applied when called from a collectionfilter without the user having make this setting manually

Another option would be to merge fieldcollapsing as a feature of collectionfilter since discoverability of these plugins is low and both plugins relate to custom search pages.