donation-v3.0.0

Motivation: Allow FT donations on Donation contract, and reduce storage costs for donations while making storage more predictable.

• Adds a very basic implementation of storage standard to facilitate FT donations, where deposit to store donation is required before ft_transfer_call is called.
• Adds ft_on_transfer method to facilitate FT donations
• Handles success/failure of donation & fees transfers, rolling back donation if necessary (uses next_donation_id to avoid overwrites)
• Stores amounts as integers internally instead of strings, making donation storage lower and more predictable
• Introduces ephemeral DonationExternal struct to convert amount integers to strings for return values / view methods.