Fix anchors for table of contents.
Add a few missing words.
Deletable more cautious about ContentGroup removal

* ContentGroup was always being referenced, even for Deletables without
  any .contentgroup_set attribute. This threw an exception when you
  deleted one of these objects (such as Announcements).  Now we'll be more
  defensive.
  (fixes #1749)
* Some cleanups to comments
Starting save button
Merge branch 'master' of https://github.com/Stanford-Online/class2go into jbau-save-button
Merge pull request #1753 from sethoscope/typos

fix minor issues in README files
Updated linux installation instructions.

- Added instructions for creating MySQL database.
- Un-hard-coded virtualenv location.  (Debian puts it in /usr/bin.)
- Moved /usr/local/bin/ path check up to support `which virtualenv`.
- Added numpy installation.
- Correction: STATIC_ROOT_DIR -> STATIC_ROOT
log error when >1 incomplete exam record found (#1729)

Would be nice to know if this ever happens in production.
Update to video child item appearance

* On video display page:
  * Child item titles are linked to the item
  * only files have a download button on the right hand side
  (closes #1738)
get_url() methods on models fixes

* Fix .get_url() methods so that they're more correct more often
Video "Additional Files" list more pure

* Change of ContentGroup.display_style default from 'button' to 'list'
  everywhere, including on the model.
* Schema migration to disallow display_style=NULL and set a default of
  'list'.
* Video display page "Additional Files" list made to use
  ContentGroup.display_style button to determine how the items should be
  rendered, but:
* Data migration to set all items' .display_style to 'list'
  (TODO: UI to enable button-mode display of items to come in a seperate
  branch)
Merge pull request #1745 from Stanford-Online/jrbl-1738-video-child-items-scary

Jrbl 1738 video child items scary
interactive autograder tests (fix #1726)
interactive ag test: bogus grader endpoint for jenkins (#1726)
Fixes #1543 -- Adds a "Save Answers" button + refactor + bugfixes

Bugfixes:
* Fixes #1764
* Fixes #1684

Refactors:
* get_or_create_incomplete_examrecord in exams/views.py
* Javascript function collectUserAnswers in view_exam.html
Button text save -> save answers
interactive autograder tests: get selenium working again (#1726)

Globally overriding urllib2 with our URL handler causes problems for
anything using urllib2 afterward.  Selenium gets bit by this, but could
have been anything.
Add error message if save fails
interactive test: add better docstring (#1726)
revert change to update_score, avoid conflict w/ jbau's refactoring (#1726)