[Cashtab] Improve switches on Configure screen

Summary:
Use large switches on Configure screen.

Upgrade the flexbox so that we get a gap between switches. Remove the SwitchContainer styled component as this overflow issue was solved by adding this into the Switch component in an earlier diff.

Test Plan: npm test, npm start and switches do not touch, looks good at widths 320px and up

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D15863