add on icon click handler

[jstrimpel]

The click handler that is being bound here, https://github.com/jdewit/bootstrap-timepicker/blob/gh-pages/js/bootstrap-timepicker.js#L42, assumes that there will be only one add on and that it should show the time picker widget. I have a case in which there are 2 add ons. One should trigger the widget and the other should clear the input. This implementation does not provide a way for me to stop the event from bubbling. I understand that this was done because you did not want to enforce an add on icon type, but it makes the assumption that there is only 1 and that this is the desired behavior.

If you want to change this please let me know and I can submit a pull request for making this behavior configurable via the options hash.