Rename primary/secondary/opacity colors to accents

[EvanHerman]

Resolves #415

Description

As mentioned in the original issue, it is not clear what significance the Primary, Secondary and Opacity colors have and should actually be accent colors. This PR changes the Primary color to Accent 4, Secondary to Accent 5 and Opacity to Accent 6.

Screenshots

Testing Instructions

• Edit the global styles.
• Click on 'Palette'.
• Hover over each color to see their name appear in a tooltip.

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Co-authored-by: EvanHerman <[email protected]>
Co-authored-by: richtabor <[email protected]>
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[richtabor]

@EvanHerman we'll need to do the same in the style variations within /styles/*