Bug 11161: Relabel 'child fund' to 'sub fund' in staff interface

Bug 11161: Relabel 'child fund' to 'sub fund' in staff interface

It was noted, that 'sub fund' might be a better term to use than
'child fund'. So this patch changes it.

To test, check with and without patch:

- Add a budget in acquisitions
- Add a fund in acquisitions
- Add a sub/child fund to your fund (label of menu item #1)
- Edit your first fund, check option to update owners of
  sub/child funds (#2)
- Try to delete your 'parent' fund (tooltip #3)
- Click on the greyed out entry (alert ÃÃ#4)

If you like the change, please sign-off. If you think otherwise,
please comment on the bug report.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>