Update ThemeKit version and changelog for new release

[d-koval]

Updating to v1.2.0. The new version will be compatible with the Theme Kit access app.

Warn Checklist

• [ ] This changes the interface and requires a Major/Minor version change.
• [ ] I have :tophat:'d these changes by using the commands I changed by hand.
• [ ] I have added a dependancy to the project.
• [ ] I have considered any potential impact on node-themekit