Yak shave for interaction_data. Ensure timestamp, lang, etc are always sent in interaction data.

* Removed the .interactionData namespace from storage.js, created our first model - shared/models/interaction_data.js
* Simplified how data is stored into interaction_data, created current and staged sub-namespaces
* Added stageCurrent and publishStaged functions.
* in shared/modules/interaction_data.js, simplified calls to model.
* Tried to make the xhr mock make more sense and provide facilities usable for peeking at last XHR request data.

issue #1597