Associating MultipleChoiceSequence with VisualPrompts

Getting started on [#39902221]
Helping prompts show in the page [#39902221]
Model fixes for MC visual prompts

[#39902221] This include will probably be useful. The order of the children array is probably superfluous.
WIP on showing Initial Visual Prompts in MC Seq

[#39902221] This shows the list of prompts but doesn't include the toolbar.
This adds the controller actions for the toolbar

[#39902221] My mistake was in assuming the problem was in DryML. In fact, I needed to ensure the controller actions were in place to support the links the tags would create. This does that.
MultipleChoiceSequences have GiveUp and Confirm visual prompts

Might as well add them all. [#39902221]
Making the spec pass (to_hash)
Finishing correct to_hash of MC with visual prompts

[#39902221] ready to go!
Updated expected-output for MC sequences

[#39902221] Also, one little bug fix found by the tests.
Merge branch 'master' into staging