I've split this into a separate task because donor-facing branding would be the most urgent to change.
Note that branding must not be changed before January 15th.
- We don't have any images which include the GC logo, so nothing to do there.
- Two i18n strings need to change: donate_interface-globalcollect-proxy and apihelp-donate-param-gateway.
- TODO: Determine whether we consider the URL "Special:GlobalCollectGateway" to fall under the branding agreement.
- Talk to Ingenico merchant services about what appears on donors' bank statements.