[Cashtab] Remove legacy address display

Summary:
T1730

Remove option for user to toggle between ecash: prefixes and legacy bitcoincash: prefixes. This diff also shows the prefix and includes some css adjustments for fitting the longer address string.

Initially I attempted to deprecate all support for legacy prefixes, but this requires some additional attention in functions and unit tests and hence will be done in a different diff.

Test Plan: npm start, check the appearance of address on home screen, toggle to eToken, check appearance, note any aesthetic complaints or responsiveness issues

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9881