Point header school logo to external site

For GiveCampus school settings.

The shared header links the logo to the school landing page. The school/campaign branding setting Do not link logo to school landing page disables that link; it does not offer an arbitrary replacement URL. Use an explicitly configured page-content link for the external website, or ask support to review the specific header. A school-page redirect would affect other visits too and is not a logo-only setting.