Add config option to list names, amounts, comments of people who gave
e.g. shows public list of last N people to give. "£30 from Rich: love what you are doing, keep it up!" type thing.
- needs config option, if enabled, the public form will offer a checkbox "show my first name, amount and message publicly"
- needs to store this opt-in with contribution
- needs to export last 5 donors who opted in in getInitData
- (later: add config option for number of recent donors to show)