Fixes #765 - single => true' on facet now works on "more" screen

[eranhirs]

Fixes #765
The bug was:
In :solr_facet_params which queries solr when opening the more window, we do this:

# Now override with our specific things for fetching facet values
solr_params[:"facet.field"] = facet_field

The problem is that we override logic that :add_facetting_to_solr is doing for special usecases like query facets, pivot facets and more..

The changes are:
*1 - Seperated some of :add_facetting_to_solr logic to a new method named :handle_advanced_facets
*2 - Now I can call the :handle_advanced_facets method also from :solr_facet_params
*3 - In the overriding line I changed facet_field from single value to an array

The fixes:
*1 - as described in #765.
*2 - this will fix many problems with the 'more' screen we didn't reach.

[cbeer]

I'd like to take a closer look at this and hopefully will have more comments, but before merging this PR should:

• be rebased
• have the indentations fixed (I'm not sure if you're using 4 spaces, a hard tab, etc.. I think our style is just 2 spaces)

[cbeer]

Is it possible to re-use #add_facetting_to_solr in its entirety? I think there's some other stuff going on there that we might want too.

[eranhirs]

What I wanted is to reuse :add_facetting_to_solr by sending the field_name with user_params, then in :add_facetting_to_solr return only one field in solr_params[:"facet.field"] if field_name is set.
This way we can delete the override line in :solr_facet_params.

To do that:
*1 - we need to refactor some more code, for example:

solr_parameters.append_facet_fields blacklight_config.facet_fields_to_add_to_solr

flattens to an array all the facet_fields, we need to change it too.

*2 - I think there is nothing more we need from :add_facetting_to_solr

[eranhirs]

Quite a mess with the indentation, I fixed it for the whole solr_helper.rb which made a lot of line changes.
Is it clear like this or should I fix it only in my code?

[cbeer]

Replaced by #777

[cbeer]

@eranhirs I've replaced this with #777, which fixes the same problem and fixes some other problems with the catalog#facet action too. Thanks for the contribution and the bug report.

[eranhirs]

Great as long as the bug is fixed! Thanks :)