Add CategoryItemMetaKey model and admin.
Add related_name for Category.parent.
Fix admin search bug.
Fetch Category's raw_item_metas as dictionary.
Add category image onlyif exists.
Display and response to filter options.
Revise API for filtering store_items with query.
Request API with query.
Only output script if has raw_item_metas.
Refactor to wrap filter options into query's filter param.
Merge pull request #26 from gregwym/filter

Add filter to store category page.