[e.cash] Update Wealth Redefine Copy & Page

Summary:
The copy of "wealth redefined" is out of date and provides no useful insights.
Since ""wealth redefined" is not our slogan anymore and the landing page has no informative copy either,
I suggest repurposing the "wealth-redefined" page into a "What's eCash" page.

Reasoning:
People visit the website to get basic information about the chain. Most people I talk to have no idea about the core technology behind eCash. Short references to "Avalanche" makes it also look like something built on an AVAX subnet or something (multiple people told me they thought so by now). With the basic info page we can introduce our core tech, value proposition, inspiration, and team, with suitable buttons on some paragraphs.

The Button in the "about" tab needs to be renamed, as well as the link from wealth-redefined to whats-ecash.

Test Plan: Visit e.cash/wealth-redefined and check the copy. Suggest potential improvements.

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman, johnkuney, Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D16619