Update theme settings

[jasonnrosa]

Types of change

• [ ] Bug fix (change which fixes an issue)
• [X] Enhancement (change which improves upon an existing feature)
• [ ] New feature (change which adds new functionality)

Description

Updating theme settings to follow new recommended UX patterns. I also added some additional theme settings and tried to clean things up a bit. This also swaps out old settings for new style fields (e.g. border, spacing, etc.).

Relevant links

Fixes #308 Fixes #92 Fixes #360

Checklist

• [X] I have read the CONTRIBUTING document.
• [X] My code follows the style guide requirements.
• [X] I have thoroughly tested my change.

People to notify CC: @TheWebTech