Feature request: add roll option to advanced position menu

[cheater]

Please add the option to roll by +/- 360 degrees in the advanced position menu. Please also add it to the controller bindings screen.

Roll means turn around the axis pointing straight out in front of you. Please consult this image:

https://www.novatel.com/assets/Web-Phase-2-2012/Solution-Pages/AttitudePlane.png

Apparently a lot of headsets have a bug where they think gravity is turned a little in the roll axis, and I've become painfully aware of this when my headset started doing that recently. So I would really appreciate it if we could implement this as the next thing.

To clarify: the camera view should be rolled after the rotation which stems from the head tracking has been applied.

[cheater]

The feature kind of works, but there are the following issues:

1. the step size on the slider bar is too large. The slider should have slower steps. I'm not sure how to do this with the GUI, but we need to be able to change the angle with finer steps.
2. the number above the slider doesn't display anything. It should display the angle with three decimal points (eg -22.785).
3. After doing an adjustment and leaving the position menu, when you re-enter the position menu, the slider gets reset to all the way right (making the image upside down).
4. The binding for Roll Left / Roll Right is way too slow. It should be like 4x faster (was previously: 10x. but that would be too fast). This is one of the reasons we need analogue controls from the joystick - this way moving the joystick just a little will roll very slowly, and moving it a lot will roll very fast.

[cheater]

After using this for a little bit more, I've found the following:

1. The speed is actually okay. We only ever need small adjustments anyways. It could be 2 or 4x faster, but 10x would be too much. So I updated point 4 from the previous comment to be 4x, instead of 10x.
2. When I said the step size is too large, I mean the step size on the slider bar. The step size when using the controller binding is fine. So I updated point 1 from the previous comment to reflect that.
3. Bug: if I use the controller to roll, and then use the controller to tilt the camera angle up or down, the roll gets completely reset.
4. Bug: the roll also gets completely reset when entering the menu by pressing A on the controller.

[cheater]

Just tried the newly uploaded 4.812 (not the previously uploaded 4.812 from yesterday). Please could you make the following changes:

1. Make the speed of roll 2x faster than it is now
2. Bug: when you set the value of roll, you clamp it in code to between -180 and 180. However, when the user opens the advanced position menu, then the value gets clamped to between 0 and 180. Which means that negative values get set to +180 degrees. Please check this in the code and make sure that negative values of roll can be restored.