FEATURE: Ability to exclude category from search results. (#7194)

This commit also adds `Category#search_priority` which sets the ground
work to enable prioritizing of posts for certain categories when searching.

app/controllers/categories_controller.rb

@@ -293,6 +293,7 @@ class CategoriesController < ApplicationController
                       :default_top_period,
                       :minimum_required_tags,
                       :navigate_to_first_post_after_read,
+                      :search_priority,
                       custom_fields: [params[:custom_fields].try(:keys)],
                       permissions: [*p.try(:keys)],
                       allowed_tags: [],