WIP on interactive-scrolling bug: rewrite. [#59668812]

This handles most cases, but is still far from perfect for ImageInteractives, and doesn't do well with iFrame interactives which resize themselves on load. (In both cases, it fails to correctly figure their height, and therefore when it should start and end pinning.)

https://www.pivotaltracker.com/story/show/59668812
Getting jasmine-jquery from a gem, not direct d/l
Conflicts:
	Gemfile.lock
Failing spec test for Embeddable::Answer module.

I was looking at this, because there seemed to be an attempt to memoize
the result of prompt_no_itals into class vars.

This isn’t currently happening, but in addition to that, this prompt_no_initials
isn’t doing what we thought anyway.

One idea is to just remove references to @@cleaned_prompt?? TBD
Fixing spec for scrolling interactive; green now
Gets a more recent version of jasminerice

Needed to get Jasmine 1.3.1 in the test runner. I'd like to take jasminerice out of the chain if I could.
A little better setup for waypoints testing
Pinned interactives that work! [#59668812]

Instead of trying to handle images differently from other Interactive types, this solution simply does the naive setup of objects and the waypoints as though the Interactive is at its final size, but then it sets up a timer and runs, at intervals (every 2.5 seconds at the moment) a script which checks to see if the height of the Interactive has changed. If it has, all waypoints are cleared and re-set. (Because setting the waypoints checks if pinning is still appropriate, they won't be set if the Interactive is now too tall.)

I would prefer to listen for an event (e.g. onresize) generated by the changing size of the Interactive div, but there isn't such an event for div elements in Javascript at the moment.

https://www.pivotaltracker.com/story/show/59668812
Stop the height-watching interval if height is fixed.

[#59668812] If the script watching the Interactive height goes three times without seeing a change, it shuts itself off.

https://www.pivotaltracker.com/story/show/59668812
Implements an HTML validator for models [#60459320]

This rejects updates to some models if their HTML fields aren't valid, using Nokogiri's XML parser to judge validity. This prevents a situation where broken HTML stored in a model can break page rendering (and become impossible to fix by also breaking the editor.)

https://www.pivotaltracker.com/story/show/60459320