Version bump to 4.0.0

Version update to 3.9.1

Update stable tag

Bump versions for 3.8.1

Update version in style.scss

Update pot version to 3.7.0

Update versions and changelog to 3.6.0

Prepare version changes & changelog for 3.5.1 release

Prepare version changes & changelog for 3.5.0 release

Update changelog with links for 3.4.0 release.