[e.cash] Add brand page content

Summary: Adding the logos, colors, and fonts to the brand page

Test Plan:
preview the site and go to the ecash brand page
check all the content looks good on mobile and desktop and both themes and that the links work

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D13931