Migrate to GPUImage 3

[alex-taffe]

We're currently using GPUImage which hasn't been updated in 3 years, and also uses OpenGL, which is deprecated. GPUImage3 is written in Metal and Swift, and is actively maintained

[alex-taffe]

The ultimate goal according to the developer of GPUImage is that GPUImage2 and GPUImage3 will be identical in terms of API, however 3 will be metal based and 2 will be OpenGL based. As of right now, 3 is still missing key functionality like motion detection filters. 2 is also incomplete, for example, it is not yet possible to change the camera from front to back or the orientation of the video feed because the variable is implemented as:

public var location:PhysicalCameraLocation {
        didSet {
            // TODO: Swap the camera locations, framebuffers as needed
        }
    }

As a result, this has to be put on hold