[e.cash] Add core tech

Summary:
Adding the core tech features to /tech page
Note: still waiting on some icons for each, just using a placeholder for now

Test Plan:
preview and check copy. Copy was pulled from e.cash/core-tech and
condesed and made some bullet points

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: Kronkmeister, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D18440