Refactor topic models (bigun)

See 0117 for a good overview.

ProjectTopicContainers (god what was I thinking) => Topic
Topic => LegacyTopic
TopicNodeAssignment => TopicAssignment

Lots of refactoring in any file that referenced anything about topics.
Merge pull request #162 from editorsnotes/dev

Major changes just about everywhere, highlights:
* Models are specific to projects; topics are split between project-specific topics and Topic Nodes, which connect those referring to the same entity
* Custom user model
* Project-level permission system
* JSON API with Django Rest Framework backend; interacted with in a Backbone.js-driven frontend
* ElasticSearch for searching (& more)
Merge branch 'master' into change-topic-models

Conflicts:
	editorsnotes/main/views/notes.py
Merge pull request #163 from editorsnotes/change-topic-models

Refactor topic models (bigun)
Take out remaining explicit link in index page
Fix topic template rendering

Pass view args as model objects, not dicts retrieved from elastic
search.
Add breadcrumbs to notes, topics, documents
Make document description text prominent (is it too prominent?)
Show how many related notes a document has in tab marker
Restyle breadcrumbs
Fix transcript admin links
Fix note links in topic template
Fix project-specific all-{notes,documents} pages
Merge pull request #164 from editorsnotes/little-things

Little things
Only show project info on all-* pages if present
Merge pull request #165 from editorsnotes/little-things

Only show project info on all-* pages if present
Use elasticsearch to find common item types, not haystack
Make default license 'all rights reserved'
Fix typo
Fix more typos in topic node page