add app3 to multitail-prod
Profiling and improving left_nav generation

* Small refactorings to leftnav(), get_full_contentsection_list() and
  lef_nav.html to try to reduce the number of SELECTs. Current runnig
  count 1200->810.
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-work
cache stats should print hourly, not every two min
Fix for #1894.
Add prev/next btns for navigating sections #1849
Minor code cleanup
Fixes many left nav problems:

Mainly, puts context back so that it will hightlight where the student
is and also refactors and cleans up the code a lot.  Maintains the
ajax-loading and caching. closes #1746 and closes #1843

Also closes #1584 by putting them back in for exams / surveys / quiz
Merge pull request #1893 from Stanford-Online/sef-work

Print cache stats to django log hourly instead of every two minutes
fix div by zero error in cachestats (#1901)
Merge pull request #1902 from Stanford-Online/sef-1901-div-by-zero-in-cachestat

fix div by zero error in cachestats (#1901)
Merge pull request #1900 from Stanford-Online/jbau-jrbl-refactoring_left_nav

Jbau jrbl refactoring left nav
Merge branch 'master' of github.com:Stanford-Online/class2go into kluo-1849-section-nav-links
Get sections from common_page_data
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
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