[Cashtab] Adding airdrop hex prefix and OP_RETURN msg to airdrop payments

Summary: As per T2288, updated Send component and useBCH hook to detect an airdrop payment and adds an airdrop standard prefix and message to the OP_RETURN output.

Test Plan:

• npm start
• send non-airdrop one to many XEC Send with no message and verify no OP_RETURN output.
• send non-airdrop one to many XEC Send with a message and verify the following OP_RETURN output:

OP_RETURN
_tab
the message

• generate an airdrop, click on the Copy to Send Screen button, then send without a message and verify the following OP_RETURN output:

OP_RETURN
drop
_tab

• generate an airdrop, click on the Copy to Send Screen button, then send with a message and verify the following OP_RETURN output:

OP_RETURN
drop
_tab
the message

• ensure no regression with the encrypted (etab in place of _tab) and unencrypted one to one transactions.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11382