`jQuery.UIkit.$html` property added.
Subscription for events like `UI.$doc.on('event', 'element', func)` and corresponding `.off()` changed to `UI.$html.on('event', 'element', func)` in order to fix incompatibilities with [Polymer Platform](https://github.com/Polymer/platform).
Removed unused `winwidth` variable in `offcanvas.js`.
Removed unused `eleheight` variable in `smooth-scroll.js`.