Bug 21695: Clean up access files template

Bug 21695: Clean up access files template

This patch modifies the access files template to help
compliance with several coding guidelines:

- Bootstrap grid
- Improve DataTables configuration
- Move date formatting from the script to the template
- Markup corrections

To test you must modify koha-conf.xml to contain something like the
following:

<access_dirs>
    <access_dir>/tmp/koha-public</access_dir>
</access_dirs>

Make sure the directory exists and contains multiple files.

 - Go to Tools -> Access files
 - Confirm that the page looks correct and the layout adjusts at various
   browser widths.
 - Confirm that DataTables functionality works correctly, including
   correct sorting by date.

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>