BREAKING CHANGES:
`$bar-button-wp-color` was renamed to `$toolbar-wp-button-color`
`$bar-button-wp-border-radius` was renamed to
`$toolbar-wp-button-border-radius`
Added `$toolbar-wp-title-text-color` for better control of the title
color
Removed `$toolbar-wp-button-color` from the default themes
references #6364