notify user of any errors in saving.
refactoring code to be a bit DRYer, fixing bug in topictree rendering.
refactoring JS code to use better names, common function to show API messages.  Removed outdated logic for view-based notifications, which broke once caching was implemented.
made messages more shared and compact, and made sure related error messages displayed to the same client-side message ID--to avoid multiple messages on the same page, with similar messages.
fix type-o in exercises; make show_api_messages more robust (so that when it blows up, it does so in a more reasonable way.
ignore validation errors in UserLog; they can't be handled.
organizations mail validation
organizations mail validation
use a separate (memory-based) cache for sessions
message update
Merge pull request #332 from bcipolli/ignore_userlog_errors

ignore validation errors in UserLog
@rtibbles No queries, so no need to wait?
remove pdb, and debug should be DEBUG
Hooked up already existing text box
add hide options
The error messages will be red now.
Merge pull request #338 from ruimalheiro/illegalemail

organizations mail validation
Super cool, works great, and so simple!
don't show 'struggling' in key when showing videos.
restored additions from previous commit; updated for polyline cleansing
updating json files
Reversed order of link and text box. Style attributes in headcss. input box is readonly