Add Support for custom CSS for Widgets and Alerts

[tmarkn]

Allow users to optionally stylize their own layouts using CSS for more customization.

Currently, with the way Caffeinated handles adding to OBS, it adds the Widgets using iframes that you can't add CSS to.

Allowing CSS either through OBS or directly through Caffeinated, for Chat specifically, would help a lot in making it fit better on their stream layouts. And maybe it can be extended to the other Widgets and Alerts.