Added unfocused window border colour changing

[CodeAndGin]

Added functionality to have a secondary border colour for unfocused windows

Gonna be honest here - this was a project in frankensteining unfamiliar code in an unfamiliar language with an unfamiliar API, so while it works on my machine just fine, it could probably do with a look over and refactor if necessary, cuz once I figured out where to put the required logic, I just grabbed the uniform update function from elsewhere and plugged it in.