Bug 23109: Improve description of staffaccess permission

Bug 23109: Improve description of staffaccess permission

Changes:
Allow staff members to modify permissions for other staff members
To:
Allow staff members to modify permissions and passwords for other staff members.

As suggested by Andre on the initial bug report.

To test:
- Go to any patron account and check More > permissions
- Veriy the description is shown as noted above
- Apply patch and run database update
- Reload the page and verify the description has changed
- Run the following SQL and verify the description in the
  database table matches as well:

SELECT * FROM userflags where flag = "staffaccess";

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>