Only allow drag scrolling if there is scrolling available
Fix toolbar on device

For some reason, touching toolbar elements only generates touchstart and
touchend events, and not click events.  Luckily, UI.button(id).click()
abstracts this away and gets things working both on the desktop and on
the device.  I thought I had tried this before without it working, but
it seems to be good now.

Ref. #9.
Kludge to fix back button in toolbar

As noted in the previous commit, there are no click events for the
toolbar on the device.  But the SDK only assigns a click listener for
the back button.  Here, we add the robust handler via UI.button.  Note
that this will fire after the build in one (if it's triggered), so we'll
end up popping two pages off the stack if we ever have three or more
pages on it.  See LP #1302284.

Closes #9.
Add scrollbars for puzzle

These are just to show you where you are; you can't interact with them.
Note that animation is now indicated on the #grid; the various things
that are animated look to this to decide what to do.  Because of this,
we've taken out the event handler to remove the animation class.  We
didn't really need that anyway.
New toolbar icons

Closes #11.