Store: Fix a NameError on vcs_update
Docs: Improve the release notes index page

Moved the upgrade notices from changelog to release notes index, included
a link back to changelog from release notes index, and changed to
link to TTK release notes instead of changelog.
Docs: Move 2.1.1 changelog to release notes

This way all the releases that can be directly upgraded to latest release
now have release notes, that are much more detailed than previous changelog.

The release notes were retrieved from SourceForge.
Docs: Add more detailed upgrade instructions
Docs: Remove unnecessary upgrading instructions
Include the assets rebuilding in setup management command

This saves us a step in installation/upgrade docs.
Revert "releasing: use mktmpenv"

This reverts commit c32a3935b5fdbffc0b43c62e54d5a3236a3f654e.

Since your virtualenv might be a around a little lets rather use a named
virtualenv.
docs: clear up we're in a venv
Unit: Update quality checks at the appropriate time during .save()