[POLISH] Removed unneccessary sheet references
[FEATURE] adding two more math Formulas
Merge pull request #1 from Learnosity/feature/add_math_formulas

[FEATURE] adding two more math Formulas
[FEATURE] Initial work on data api demos

This commit has ace editor embedded, committing it in case we want it
later. Removing in favour of simply rendering JSON.
[BUG] Fixed broken questionEditorDemo:
- bad use of fixed_preview UI option.
- demo referencing to response editor (should be question editor).
- the element wrapping the iframe (.learnosity-question-editor) MUST be a div in order to have fixed_preview working (was a span).
[COPY] Adding point to asset example on editor
[FEATURE] data api demo integration

Added xhr proxy to make requests to the data api
[FEATURE] Added more data api endpoints

Now have:
 - itembank
 - schools
 - users
 - sessions
[REFACTOR] Cleaned up data api demos

Fixed issue where request was being POSTed even when we had no
params to send.

Used better default data in parameters.

Removed redundant filter options for endpoints where they made
no sense.
[FEATURE] Added security and request keys to JSON request
[BUG] Removed debug output
[FEATURE] Add Items API Adaptive demo

Currently pointing to staging environment as production setup is being finalised
[REFACTOR] Initing Items API into variable
[POLISH] Added Number line, Plot Rays, Plot segments, Plot vectors, Plot Circles to questionsapi demo.
[POLISH] Updated questioneditor asset request example.
Fix type
[FEATURE] Added sessions/statuses endpoint demo
[BUG] Removed broken  flag logic
Update index.php
[CONFIG] Now pointing at v0.21 of the data api