Bug 25675: Reword and reorganize sysprefs related to patron self modification

Bug 25675: Reword and reorganize sysprefs related to patron self modification

To Test:
1: apply patch
2: restart all
3: go to System Preferences > OPAC
4: confirm "Self registration" section is now labeled "Self registration and modification"
5: confirm OPACPatronDetails is now in the "Self registration and modification" section
6: confirm PatronSelfRegistration now reads "(Allow / Don't allow)  library patrons to register for an account via the OPAC."
7: set OPACPatronDetails to Don't allow
8: set PatronSelfRegistration to Allow
9: log into the opac and verify you're not able to edit your patron details on an existing account

Signed-off-by: DonnaB <donna@bywatersolutions.com>

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>