Move all theme related color codes to theme .css files

[sparky8251]

For some reason, several UI colors are stored outside of the theme folders. Not only does this cause color clash, it makes it impossible to make custom themes without building from source.

For examples, see this, this, and this.

You can find these "emby green" spots in the source by searching for 52b54b, 82, 181, 75 (which is the same as the previous hex), 5EC157, 2bc253, and 54f054.

These codes might change if a branding pull is merged.

[sparky8251]

Finding additional places that colors are hard coded, like the login page.

[jellyfin-bot]

We are moving all feature and enhancement requests to our new Fider platform here. This new platform lets people vote on and better manage such requests.
This request now lives here.