Bug 29057: Use font awesome icons on request.pl

Bug 29057: Use font awesome icons on request.pl

This patch offers an alternate take on using Font Awesome icons on the
holds page in place of images as links.

This revised patch updates the icon implementation so that it is easier
to override the Font Awesome icon selection with CSS. Test by adding the
contents of this file to the IntranetUserCSS preference:

https://gitlab.com/-/snippets/2319364

To test:
1 - Place some holds on a record
2 - View the 'Holds' tab in the staff interface
3 - Note the new icons
4 - Note their hover test
5 - Confirm the buttons still work as expected

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>