Combat Overlay implementation

[aymeric-giraudet]

Replicate what's done on the original overlay app
I think creating a new Electron window with a different html file from the main window would be better as it would allow users to place the combat overlay wherever they want and it doesn't share any state with the rest of the app so that's alright

[aymeric-giraudet]

After some thinking, I've decided that maybe refactoring dialogManager further is not that important as it won't need too much maintenance anymore.
Priority should definitely be on the combat overlay ! So I've started working on it, style and ergonomics need some polishing and I still need to implement the filters.
After that it should be a breeze I think.

Pinging you @mikerollins to let you know :)