LinkDrop contract

LinkDrop contract allows any user to create a link that their friends can use to claim tokens even if they don't have an account yet.

The way it works:

Sender, that has NEAR:

• Creates a new key pair (pk1, privkey1).
• Calls linkdrop.send(pk1) with attached balance of NEAR that they want to send.
• Sends a link to any supported wallet app with privkey1 as part of URL.

Receiver, that doesn't have NEAR:

• Receives link to the wallet with privkey1.
• Wallet creates new key pair for this user (or they generate it via HSM) (pk2, privkey2).
• Enters the new_account_id receiver want for their new account.
• Wallet creates a transaction to linkdrop.create_account_and_claim(new_account_id, pk2).
• Contract creates new account with new_account_id name and pk2 as full access key and transfers NEAR that Sender sent.

If Receiver already has account (or Sender wants to get back the money):

• Sign tx with privkey1 to call linkdrop.claim(), which transfers money to signer's account.