Support persistence to / from AI Desktop doc format

[eb1]

Currently the adaptation content is scaffolded in memory for our in-house testing. There is an open issue to track (issue #11 ), but it would also be advantageous to allow users to load from an existing AI desktop project directory, or save their existing work to the AI desktop format.

This issue is to investigate the persistence to / loading of adaptation content from the Adapt It desktop document format.

This issue -- like #11 -- is a larger development item, and might need to be subdivided into separate components for KB, document and settings files.

[eb1]

Split this issue out into #53 and #54. Closing this one as it's a bit too vague.