Add ability to preview UI elements to see cosmetics editor changes.

[leggettc18]

It would be a good idea for the Cosmetics editor to be able to show a preview of UI elements that aren't always on-screen. For example, Timers, Keys, Maps, Carrots, etc. This would be especially useful for, say, the margins on a timer, as then you can edit them without needing to be in an area that has an actual timer running.