wq/app.js+wq/store.js: better handling of formdata in offline storage

[sheppard]

Need a general solution for ensuring FormData is not lost when round-tripped to localStorage (see comment in wq/app.js).

Solution should ideally work both in the browser and in cordova, but will need a way to save files and/or file references in offline storage. May need to leverage another storage mechanism and/or another library - see #20 and @jeremiahsa's localstore library.