Add camera collisions about godot-trackball-camera

[Goutte]

The first thing I'd try would be to add a Collision Shape as child of the Camera.

Since we're swapping the Transform of the Camera, I don't think it plays very well with collisions.

Perhaps by rewriting the function differently ?
Always setting the angle from the position, and letting the collision engine handle the position (using a Spring around the target, so that the Camera "slides" on walls neatly — means the zoom shenanigans are to be tweaked too) ?

Sadly i have some health, work and money issues to tend to, and I don't have the leisure to try my hand at this. You're welcome to try and push a merge request, though !

[Goutte]

Perhaps there's a simpler way, but dumber : in apply_contraints(), check if the new position is in the walls, and if it is, push it out.

Probably inefficient, but perhaps there's a way.