DLTP-232 Adding datepicker for date created field

Set multiple to false for date_created
Merge pull request #49 from ndlib/DLTP-232

Adding datepicker for date created field
Updating File Upload notice

We do support larger files, but it requires special assistance. The
previous message was confusing, whereas this message is direct.
DLTP-227 File Thumbnail changes.

* The thumbnail/representative image on a work should be clickable and
  when clicked direct the user to the downloaded file for that
  representative file.
* On index page thumbnail should link to show page for curate concern.

dltp-227#

Fix file selection for link on thumbnail to representative image instead of just the first one.