The vendored CSS required by `react-tippy` is now imported instead of
inlined. This should result in no functional changes, and it makes it
easier to lint our styles.
This was originally inlined in #3120 when `react-tippy` was first added
to the project. It has not been updated since then, so I don't think
there's any risk this has gotten out-of-sync.
* Use tooltip for display of helper text in wallet views copy to clipboard feature.
* Use react-tippy in wallet-view.js; center arrow tooltip throughout tooltip text change.
* Remove unnecessary tabIndex attribute from wallet view address element.
