[Cashtab] Move collapse styled components from Tx.js to StyledCollapse.js

Summary: Related to T2375. Moved Tx collapse styled components from Tx.js to StyledCollapse.js so the SCs can be reused elsewhere in the app.

Test Plan:
cd web/cashtab && npm start
observe that the Tx collapse still works

in StyledCollapse.js - observe that the Tx collapse styled components are now exported from StyledCollapse.js.

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11295