FormWidget: add note that this.focusNode must be a sub-node rather than the root node.
Container: remove getPreviousSibling() and getNextSibling().
Can just use Element#previousElementSibling and #nextElementSibling.
fix tabbing in less files, fixes #196
Add d-hidden and d-invisible classes to global.less,
plus d-hidden, d-shown, d-visible, and d-invisible
attribute selectors to be used in templates.

Thought about putting the attribute selectors in a CSS file automatically
loaded by handlebars.js, but just putting theme as part of the theme for now.

Fixes #197.
Setup dependency on jQuery.
Convert CssState.js to use jQuery DOM class methods.
Convert focus.js to use jQuery class methods.
Convert HasDropDown.js to use jQuery DOM class and manipulation methods.
Convert place.js to use jQuery DOM manipulation methods.
Convert Widget.js to use jQuery class methods.
popup.js: use jQuery rather than dojo/dom* modules