Adding, linking and revoking donor declarations

Declarations should be kept up to date so GiftAider can make clearer decisions during validation and claim preparation.

1. Add the declaration to the correct donor.
2. Record the date signed.
3. Choose the declaration method, such as written, email, web or SMS where available.
4. Link the declaration to relevant donations where the workflow allows it.
5. Revoke declarations that no longer apply.
6. Review affected donations before preparing a claim.