[Cashtab] Improve styling for settings items

Summary:
These were added incrementally and did not follow a standard pattern.

Remove classNames and use parent component, so that all have the same styling.

Remove obsolete display:none for auto camera open setting, as this is now conditionally rendered with isMobile

Shorten label for hide msgs as it crowds out the switch on smaller devices.

Test Plan:
npm test

desktop:

mobile:

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15563