Add prev/next btns for navigating sections #1849
Minor code cleanup
Merge branch 'master' of github.com:Stanford-Online/class2go into kluo-1849-section-nav-links
Get sections from common_page_data
Caching the complicated pieces of common_page_data

* left_nav generation isn't the real problem, the real problem is
  common_page_data. So now we address that directly, and add some caching to
  get_common_page_data for the complicated pieces.
* Current running count of SELECTs when loading left_nav.html 810->6.
interactive autograder unicode test (#1904)
interactive autograder: conv user input to ascii (#1904)
Parameterizes the login link based on class--

stanford only goes to shibboleth, public goes to class2go login.
Fixes #1908
Cleanups to leftnav refactorings and related code

* Addressing @jbau's comments on #1898:
  * Commenting out calls to CacheStat pending resolution of #1905
  * Using draft/ready in cache keys to help eliminate potential
    information leakage
  * Elimination of view_mode (nobody seemed to be using it)
  * Elimination of current_datetime and effective_current_datetime (these
    were also unused)
  * Careful testing of the appearance of leftnav, behaviour of static
    pages and exam creation
Merge pull request #1895 from Stanford-Online/dca_new_working2

Fix for #1894. csv bombs for survey csv submission generation.
Merge pull request #1898 from Stanford-Online/jrbl-refactoring_left_nav

Jrbl refactoring left nav (and top nav)
Merge pull request #1899 from Stanford-Online/kluo-1849-section-nav-links

Add prev/next btns for navigating between single sections #1849
merged master
cachestat cleanup to remove exception case (#1905)

Based on good stuggestions from @jbau.  Now cleaner and doesn't have any
uncaught exceptions.
QuizDown converter + sample files
Merge pull request #1922 from Stanford-Online/jinpa-master-quizdown

QuizDown converter + sample files
Merge pull request #1920 from Stanford-Online/sef-1904-interactive-exercise-unicode

interactive autograder protection from unicode (#1904)
Merge pull request #1921 from Stanford-Online/sef-1905-cachestats

cachestat cleanup to remove exception case (#1905)
Merge pull request #1910 from Stanford-Online/jbau-fix-login-links

Parameterizes the login link based on class--
say who wrote it