Improve navigation & structure of documents

Presently, the new RTD contents list in the sidebar is more or less unusable:

https://www.dropbox.com/s/bl36v087cza6r7v/Screenshot%202014-07-14%2014.48.21.png (image)

The new version looks like:

https://www.dropbox.com/s/soiv9iq4vss1v9k/Screenshot%202014-07-14%2014.49.50.png

The expanded table of contents still appears in the main index page.

conf.py has also been updated to use the new RTD theme locally, if the user has it installed; if not
it will use the built-in theme as usual.

Also includes miscellaneous minor corrections.
Backports documentation restructure from develop

Commits:

52a480beec529955cf2ebbd618666520c238ad39
ea6e46ef874a76b9eebd8d7de8db6782f1d01806
Merge pull request #3307 from evildmp/documentation-backport

Restructure documentation and improve contents tables (backport)
Fix docs building
Merge pull request #3313 from yakky/feature/fix_docs_master

Fix docs building on master
Fix location of breadcrumb template in docs

`breadcrumb.html` is actually located in `menu`, not `cms`.
Merge pull request #3369 from derek73/patch-1

Fix location of breadcrumb template in docs
Fix PageUserAdmin for custom user model.

Don't crash at startup if the custom user model has no first_name and
last_name fields.

The PageUserAdmin still won't actually work, so you'll have to subclass
it and change the fieldsets to include the fields that actually work, but
at least you can import it now.
Modify the custom user model to have fewer fields.

Allows us to test whether PageUserAdmin works or not.
Fix tests throwing another exception during teardown.

This conceals the original error that you actually want to fix.