[Cashtab] Match hover effect for all icons on settings page

Summary: Related to T2662. Hover effects for icons in the SWButtonCtn and in the ContactListCtn are now consistent across all icons.

Test Plan:
cd web/cashtab && npm start
navigate to Settings screen
Expand the Contact List and Saved Wallets dropdowns
hover over each icon (edit, add contact, copy, delete)
Observe that each icon has the same hover effect

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D12080