Speed improvements for searching by avoiding solr queries

[cjcolvar]

Included in this PR:

• Reuse existing ability model for testing if conditional facets should load because instantiating new ability objects requires a solr query to answer the ability check instead of using a cached value.
• Use SpeedyAF::Base.for to cast the SolrDocument into a proxy when constructing a search result's title link instead of using #find which calls out to solr.

With these changes searches with 10 results per page return in about 1s vs. 3s and 4s vs. 20s with 100 results per page.

[masaball]

Looks good to me

[joncameron]

10 results per page return in about 1s vs. 3s and 4s vs. 20s with 100 results

Nice!