Added demo page for jQuery Mobile 1.4.

Fixed focus issue in extension-mobile.
Fixed issue with startup() not creating $preview or checking the builtLayouts cache.
Added null check of $keyboard before calling .hide(), to avoid null exception if the keyboard has been destroyed.
Added back 'return container' to buildKeyboard.
Merge pull request #234 from BrandonLWhite/working

Some bug fixes and a jQuery Mobile 1.4 demo/test.