Support facets form

[andybroomfield]

Support the facets form module to allow multiple facets to be seletected without submitting the page.

Currently clicking a facet will cause a page reload (because AJAX support won't work until we upgrade to facets 3).

However it may be useful to allow users to select multiple facets first before filtering the list.
Enabling facets form however breaks the layout of the facets as it presents them differently (the groups arn't present) as it's a different facet block.