Rename the mappings feature to page_mappings

(was a little short and anonymous)
Feature for filtering mappings server-side
Mapping filter form
Add a .filtered_by_path scope to Mapping
 Avoid LIKE '%%' query in Mapping.filtered_by_path scope
Filtering should keep the filter field populated.
Filtering should also allow removal of the filter when no matches are found.
Merge remote-tracking branch 'origin/filter-mappings'