Thaw 2.1.0-rc.1

The first 2.1.0 release candidate. Nothing changed since 2.1.0-beta.6: this is the same app, promoted so it can ship as 2.1.0 if no new problems turn up. For what's new in 2.1.0, see the beta notes below.

If something breaks, please report it at github.com/thaw-app/Thaw/issues.