[e.cash] Refactor global css

Summary:
Chaging how the global styles are applied to be more consistent with styled components
-utilized styled components createGlobalStyle feature and added to the top of _app.js
-this should inject the previous css rules globally
-I moved the "container" class to be a component instead to avoid the inconsistent single classname used for that

Test Plan:
@bot preview-e.cash
See if everything renders as before

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D13866