added a condition to reinitialize timepicker if there is no mainDiv on the page. Timepicker should reinitialize if
dpDiv is removed. Otherwise it does not function correctly with for
example Rails applications with TurboLinks.
Add the button self if showOn is 'button' or 'both' and the button element is
not explicitely set.
Merge pull request #75 from kreintjes/master

Fixed issues with TurboLinks and automatically add a button if not set in options