[Cashtab][Move msg switch p2] Advanced collapse in Send.js re-titled to Message

Summary: Related to T2772. Depends on D12520. Custom msg icon added to CustomIcons, 'Advanced' custom collapse has been renamed to 'CustomIIcon + Message'.

Test Plan:
cd web/cashtab && npm start
navigate to Send.js
observe that the title of the 'Advanced' collapse is now 'CustomIcon + Message'

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12525