PEP-8 fixes for contents APIs.

library_contents.py and history_contents.py.
PEP-8 fixes for tools API controller.
Improved? (at least different) handling of library folder ids.

Move duplicated __decode_library_content_id between API controllers into UsesLibraryMixinItems._decode_library_content_id. Allow get_library_folder to take in F<id> or <id>.
Rework history.contents_iter to potentially support multiple types.
Rework history_contents API to allow room for multiple 'type's of history contents.

Only poorly named 'file' (default) is currently implemented, will use new flexibility to add 'collection' type. Room made in create, show, and index methods.
Dataset Collctions - model layer.

Mapping, model definition, database migration, and model unit tests to support database collections.
WIP: Dataset collection infrastructure glue - API and service layer.
casperjs: Centralize logic for test user login.
casperjs: Helper method for creating API datasets.
WIP: API functional tests for dataset collections.