Additional Donation Page for Partnersites

[adriancollier]

At the moment users that wish to donate from a Partnersite page are redirected from the existing domain (sometimes a custom CNAME address) to the rsr.akvo.org domain for the completion of the donation process.

In order to make this process smoother and to ensure that we retain the trust and coinfidence of the donors, we should look into adding a redirection page into the process that mirrors the process that many payment providers have when moving users from a core site into a payment process. This could be a page that automatically loads after several seconds, or a static page that requires manual acknowledgement of the progression before continuing.

[KasperBrandt]

Merged in #516

[KasperBrandt]

Test plan

GIVEN a project on a RSR Page
WHEN clicking the donate button
THEN a redirect page should be shown that redirects the user to the donations page on RSR core