bump version to 0.14.7

Summary: Bump version number, and archive release-notes.md

Test Plan: Check against doc/release-process.md

Reviewers: freetrader, deadalnix, #bitcoin_abc, CCulianu

Reviewed By: #bitcoin_abc, CCulianu

Subscribers: CCulianu

Differential Revision: https://reviews.bitcoinabc.org/D415