Previously, for a textbook with only one chapter, we allowed that chapter to
not have a title -- under the assumption that it would be shown as a monolithic
textbook, instead of a chaptered textbook. However, the UI doesn't support that
idea, the code was getting a bit messy, and there was no real benefit to the idea
of not having to specify a chapter title. This commit removes that special case,
and ensures that all textbook chapters must have a name and an asset path.

They are the defaults now

But only slightly. Sorry Christina.

Replacing the get_request_method function everywhere

Previously, when a model was deleted, the entire collection would save itself
to the server again. Now, we just call model.destroy(), which doesn't affect
other models.

Created a few RESTful API endpoints, which required creating and assigning
arbitrary IDs to PDF textbooks. Changed the Backbone views to save individual
models, instead of saving a whole collection.

Based on http://djangosnippets.org/snippets/154/

minShown = 1250, closeIcon = false