Add a 'No valid form' RapidHtml form

When RapidHtml.php can't load the requested form, instead of
showing a white screen with 'Make your donation now' title,
show an error message with a like to 'ways to donate' and the
problemsdonating email address.

Change-Id: I295fdb8dc95e0e059ef61ab9688f9cd548e46402
Merge "Add a 'No valid form' RapidHtml form"