Invert opacity setting

[Katsute]

Feature

Change the opacity setting to reflect the opacity of the background and not 1 - opacity

This is a breaking change! there are a few ways we can migrate old data:

• Add a new opacity field and migrate the existing value over. Skip if a opacity value is already set or existing is not set
• Toggleable bool to use inverted opacity behavior, set to true if the existing value is already set < have a legacy period of 6 months before we migrate and remove it (how to only run once?)

A notice is needed before this change.

Reason

To achieve parity with other background extensions and common sense