LP#1552778: add timepicker to webstaff checkout page

LP#1552778: add timepicker to webstaff checkout page

This patch adds a timepicker to go along with the datepicker
if the operator invokes the option to set a specific due
date.

To test
-------
[1] Arrange circ policies to have both hourly and daily loans.
[2] Apply the patch.
[3] Check out an item for an hourly loan. Verify that the
    due date and time is per policy.
[4] Check out an item for a daily loan. Verify that the
    due date is per policy.
[5] Check out an item for an hourly loan, but set a specific
    due date and time. Verify that the due date and time matches
    the selected value.
[6] Check out an item for a daily loan, but set a specific
    due date. Verify that the due date matches the selected
    value; note that any time component is ignored since
    for daily loans the time gets normalized to 23:59.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>