Improve date field behavior (add input mask, partial date completion)

Added jquery.maskedinput (http://digitalbush.com/projects/masked-input-plugin/)
Modified bootstrap-datepicker to turn off auto date-parsing
Added moment.js for date parsing

Extracted date field coffeescript code into its own file and added the
mask initializer, which accepts MM/DD or MM/DD/YYYY. Then added a custom
on blur handler which uses moment.js to parse the input if it's in
either of those formats. Since moment intelligently uses the current
year if it's not supplied, this allows partial date entry, i.e. 10/22.