Add collection support

[chasedog]

Adds support for:

/api/v1/collections/add_post_to_collection /api/v1/collections/collection /api/v1/collections/create_collection /api/v1/collections/delete_collection /api/v1/collections/subreddit_collections

To-do: /api/v1/collections/remove_post_in_collection /api/v1/collections/follow_collection /api/v1/collections/reorder_collection /api/v1/collections/update_collection_description /api/v1/collections/update_collection_display_layout /api/v1/collections/update_collection_title

This branch is based on chasedog:fix-build-and-update-packages. I will rebase once that's merged.