Bug 16021 - Use Font Awesome icons on automatic item modifications by age page

Bug 16021 - Use Font Awesome icons on automatic item modifications by age page

This patch revises the automatic item modifications by age page to use
Font Awesome icons instead of Glyphicons.

To test, apply the patch and go to Tools -> Automatic item modifications
by age.

- Confirm that the "Edit" toolbar button uses a "pencil" icon instead of
  a "plus." (Edit -> Pencil; Add -> Plus).
- Confirm that the icons associated with adding, editing, or removing
  rules look correct and work correctly.

Signed-off-by: Nicole C Engard <nengard@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com