major refactoring

Use RequireJS, eliminate the formdesigner singleton with controller,
model, and ui having tangled inter-references including a bunch of event
soup, in favor of well-defined coponents using events only for loose
coupling.

See https://gist.github.com/mwhite/10e42de5b24b3437a610 for additional
explanation.

This removes the recently added duplicate ID renaming on save, in favor
of, when the nodeID property is changed via a widget change,
short-circuiting the change if a sibling has the same nodeID, and then
behaving similarly to when the XPath editor has unsaved changes until
you've finished entering a valid nodeID.  In service of this, the
"unsaved changes" short-circuiting now fires on several other events
besides selecting a node:

- adding a question
- saving the form
- selecting any tools menu item
- moving a question

Currently these are all done explicitly, although it might be possible
to have fewer locations where the check is called by putting it in e.g.
beforeSerialize().

Fixes:

 - #59: use RequireJS
 - #84: choice icon in tree should change when moving from single to
   multiple answer or vice versa
make the UI self-contained, no global IDs
remove add/remove language code

it's never run
change some classes to use prototypes instead of closures for methods:

ItextForm, ItextModel, LogicExpression, LogicManager