Bug 7354: Can't edit local use system preferences

Bug 7354: Can't edit local use system preferences

Fixes adding and editing of local use system preferences and redirects to correct
page after saving.

To test:
- Create a new local use system preference
- Edit an existing local use system preference from summary page
- Edit an existing local use system preference using 'Edit'
- Delete a local use system preference

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>