feat(SensorModelling) add pixelcoordinates to CameraPoint

[RIFJo]

refers to #627

Signed-off-by: RIFJo [email protected]

#### Reference to a related issue in the repository #627

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add two integer-fields (pixel_x and pixel_y) to CameraPoint message to allow image-coordinate specification for CameraDetectionData. I chose this solution over using Vector2d (because it uses doubles) or creating a custom type "ImageCoordinates" with two integer fields - which would be another good alternative, but i was unsure where (as in "which file") such a type should be placed.

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