TAB_PAGE_USERADMIN conversion to .ui

Change-Id: I65ae56bee3e66ec0b19e40fa23ac02a8ec1afbf8
Reviewed-on: https://gerrit.libreoffice.org/10681
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>
init. pointer members

Change-Id: Iad5edda570466a35c138f7f7fe042b931c58ad75