Bug 21550: DataTables four button pagination uses the wrong icon for disabled buttons

Bug 21550: DataTables four button pagination uses the wrong icon for disabled buttons

This patch modifies the DataTables CSS which styles "full_nubmers"
controls which are disabled: First and Previous buttons on the first
page of results, Next and Last buttons on the last page of results.
These buttons should have gray icons instead of blue.

To test, apply the patch and clear your browser cache if necessary. View
a page which uses a "full_numbers" DataTables configuration, e.g.

- Administration -> Cities
- ILL requests -> List requests
- Circulation -> Holds to pull

Confirm that buttons in their disabled state have a gray icon and text
instead of blue.

Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>