Datepicker converted to event, date format, no update on change, etc.

I've extracted the datepicker call to an event. In this way people can either specify their own options, or they can implement other datepickers. I use Bootstrap and a bootstrap datepicker, so I have also provided my own event response for others to use.

In addition I added code so date fields do not update if they are not changed, updated the README, and added a few missing semicolon's etc. in best_in_place.js for consistency.

All the tests that worked when I started still work. I did not come up with an easy solution for the blur event failures in rspec. All the datepicker tests and my manual testing work.