Set flag so CODAP knows when to call on gamePhone

[#79015860]
[#79537460]
Let document save/export work when using gamePhone

This involves converting the data path from app controller’s exportDocument action down to the game context controller’s saveCurrentGameState into async-compatible, callback-accepting form.

[#79015860]
[#79537460]
Restore state during initGame when using gamePhone

[#79015860]
[#79537460]
Merge pull request #11 from concord-consortium/postmessage-save-game

Save and restore cross-domain interactives via postMessage