Adds support for facet forms

[markconroy]

Closes #633

What does this change?

Adds CSS so checkbox facets using facets forms look the same as default checkbox facets.

How to test

Follow instructions here to install facets forms.

Images

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Thanks to Big Blue Door for sponsoring my time to work on this.

[Adnan-cds]

Hi Mark,
Many thanks for such a quick pull request. It's nearly there. I would request just one improvement: a bit more whitespace between the facets groups. In the following screenshot, a little more space between the "South (1)" facet item and the "Size" facet group label would be great:

[markconroy]

@Adnan-cds can you check again?

[Adnan-cds]

Thanks, this will do:

[Adnan-cds]

Works for me. Thanks a lot :)