[Cashtab] Tx receipt icon added to Tx dropdown menu

Summary: Related to T2425. Added icon to Tx dropdown menu which user can follow to view a pdf 'receipt' of the tx.

Test Plan:
cd web/cashtab
npm start
expand a Tx dropdown from the home screen
observe the Tx Receipt label and icon
click Tx Receipt and follow the link to the blockchair generated pdf.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11455