Feature camera class

[kalwalt]

WebARKitCamera class

As mentioned in issue #21 i will implement a basic Camera class because it is necessary for the PnP computation retrieve the camera Matrix and the distortion coefficients.
For now it will calculate the camera matrix based on the width and height inputs of the camera (see setupCamera ) . This follow the OpenCV convention a matrix 3x3:

//camera matrix
[[fc, 0.0, cx],
 [0.0, fc, cy],
 [0.0, 0.0, 1.0]]

where fc is the focal length and cx = width/2 and cy height/2.
Read for more in this opencv tutorial.
The class also create distorion coefficients, 6 values, but we left to zeros.

I have implemented these member methods:
public:

• setupCamera()
• printCameraSettings()
• getCameraData()
• getDistortionCoefficients()
• getFocalLength()

private:

• setFocalLength()

In the future i will implement other methods: to load a calibration file and other utilities. I want to develop only the minimum for now: as said before, we neeed a camera matrix to compute the pose matrix with the PnP algorithm.
Tests are provided in the tests/webarkit_test.cpp file.
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