Adds sub_item_id to user_personal_collection_items, widens
collection_type to include 'playlist' and 'smart', adds media_types
filter to page_sections, moves the existing abs_playlists row into
the canonical store, and drops the abs_* collection tables.
Lays the storage foundation for the ABS adapter rewrites (collections
unify sub-project 3) to wire the application against.
