[Cashtab] Tx History collapse menu

Summary: Tapping a tx in tx history extends a collapse which reveals: a link to the tx that opens the block explorer in a new tab and a copy txid button which fires a notification when the txid has been copied to the user's clipboard. Related to task T1774.

Test Plan:
cd web/cashtab
npm start
on the main wallet tab, click on a transaction
onClick, the tx card should expand, revealing a link to the tx on the block explorer>
click on the link, it should open the block explorer in a new tab
click on the Copy Txid button, it should fire a success notification
paste the txid somewhere to ensure it was copied to the clipboard.
send XEC, check that the new transaction panel expands on click
receive XEC, check that the new transaction panel expands on click

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11111