Added datetime as a type

If the user has added http://trentrichardson.com/examples/timepicker/
js to their assests they can set a type of :datetime that adds a time
picker as well. The display_with display_as format needs to be set the
same as the time picker expects
Added tests, fixed the js

Added tests to make sure it works and also that :type => :date still
works as well.

I accidently changed the "date" in the best_in_pace.js to use datetime
so I changed that back.

jQuery-ui now comes from a Gem - not using the CSS

The slider doesn't work in this app - not sure why, could be the
ancient CSS.
Added jquery-ui-rails to the Gemspec

Without it the tests don't run at all.