Limitation by category doesn't work with Daxko back-end

[dchubar-fj]

Problem/Motivation
Activity Finder 4 provides the Limit by category setting, this setting allows you to limit results only by specific categories. But this setting doesn't work with the Daxko back-end, but only with Solr back-end. Because Activity Finder uses internal Program Subcategories NID but not Daxko categories.

Steps to reproduce

• Create a landing and add the Activity Finder 4 block
• Add any category to the Limit by category field.
• Please note the Program Subcategory nodes are used in the autocomplete
• Save your changes and check Activity Finder results.

ER: Results are filtered by the default category
AR: Nothing happens

[dchubar-fj]

Maybe sound quite simple, but in fact, the issue requires huge back-end architecture changes because Daxko logic is different from SOLR logic. I think we should use a plugin-based back-end system (described here) and each plugin should provide its own Activity Finder block settings form with logic and fields specific only for this backend.

[shelleygoetz]

@sarah-halby Jira ticked created - https://openy.atlassian.net/browse/MAINTAIN-191