Implemented datepicker in authoring forms.

Link to code review: http://mrccodereview.cloudapp.net/ui#review:id=1100

Issues:
Server rounds dates, so we can't store dates in date/month/year format. For instance, if user typed 4th of January in 1880 year then as year it will be 1881.0082191780823, however, on server side it will be rounded to 1881.01

Possible solutions:
- Return Month/Day fields in exhibit/timeline entities and use them for setting up month and day. Year can be only integer.
- Prevent any rounding on server, no further work required.