Add validation to search facets to improve UX and eliminate XSS vulnerability

[teosibileau]

Issue #CIVIC-3513

• Sets facets to be rewritable via hook_facet_items_alter in order to run filter_xss on them
• Validates content type parameter from the value provided in the url: 'search/type/<content_type>`
• Validates term ids from the value provided in the url for search/<taxonomy_field>/<format>-<tid> when taxonomy_field is either:
  • field_tags
  • field_topics
  • field_resources%253Afield_format
• Validates authors
• Validates licenses

Acceptance Criteria

• search/type/notvalid should return a 404 for everything for everything but but valid content types
• search/field_tags/notvalid should return a 404 for everything for everything but but valid term values for tags
• search/field_topic/notvalid should return a 404 for everything but for everything but valid term values for topics
• search/field_resources%253Afield_format/notvalid should return a 404 for everything but valid term values for formats
• If one of Multiple ocurrances of a facet based on taxonomies is not valid, It should return a 404
• search/field_license/notvalid should return a 404 for everything but valid license occurances
• any invalid combo of the above options should return a 404

[acouch]

This looks great. I was not able to inject text into the facets.

Should we add a test to verify that a 404 is produced?

When I visit "/search/type/notvalid"
Then I should see "Page not found"
And I should not see "Content Types"