refactor login and enrollment test cases to use the mongo modulestore

added namee to authors file

fix to problems with uploading files

Use super for calling parent __init__ methods

Refactor rake tasks for pylint/pep8

PDF textbooks in Studio

clarify LICENSE

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.