Bug 20526: Show and sort by date of request in pending discharges table

Bug 20526: Show and sort by date of request in pending discharges table

This patch adds a "date requested" column to the table of pending
discharges, and updates the DataTables configuration to sort by this
column by default.

The patch also makes some other changes:

- Table information and filtering have been added.
- The "Allow" link has been converted to a Bootstrap-styled buttong with
  an icon.

To test, apply the patch and view the table of pending discharge
requests. It should be sorted by default by date requested.

- Confirm that date sorting is correct.
- Confirm that other columns still sort correctly.
- Confirm that buttons look right.
- Confirm that the table information is correct.
- Confirm that the table search form works.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>