Fixes #4999: Allow repository creation using only the keyboard to traverse the form.

This adds an explicit blank option to account for the initial blank
being present from an empty model attribute on a new resource. The absence
of the blank leads to the position of selection being off when manipulating
the select via the arrow keys.
Merge pull request #4322 from ehelms/fixes-4999

Fixes #4999: Allow repository creation using only the keyboard to traver...