[Cashtab] Display some ideas for how to use a new amount of XEC

Summary: For users that have just earned the 30XEC reward referred from the landing page, offer some suggestions of initial eCash activities.

Test Plan:
npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D16661