CubeGizmo - add curved arrow controls and light blue color on controls when moused over

[soshochang]

Cube gizmo curved arrow controls will rotate the camera. All gizmo controls are given a light blue color when hovered over to indicate they are clickable.

[av8ta]

Hey thanks! Looks good. At first I thought it seemed like a lot of extra code for highlighting clickable faces on the gizmo but then I realised you've added the two arrows at the top for rotating the camera on the view axis. I like this addition and it works rather intuitively.

Just two thoughts:

1. would be good if when clicking a face if the camera moved slowly to position. From a human factors perspective moving slowly would allow the human brain to rotate the part mentally in time with the camera rather than have it "snap" into position. This feels jarring and might make the human doubt if the correct face had been clicked.
2. we're going to need to support touch as well as mouse. That might necessitate a different PR though!

@MattFerraro happy to merge/thoughts on this?

[MattFerraro]

@soshochang this is really cool! Amazing job!

re @av8ta 's comments:

1. Agreed, gradual movement is going to be very important for the user's spatial awareness
2. Also agreed, touch controls for everything will be huge when we want to be on iPads

But both of these are rather large tasks that I think should be in future PRs. I'm going to test it locally then probably go ahead and merge