Add a function to take a single HD photo upon button press.

[AleksanderLidtke]

Would be useful further down the line. This would probably require a dedicated method in ROVgui.py, based on rovGuiMainFrame.getNewFrame, which would release rovGuiMainFrame.cameraCapture (only have one camera), get an image of the desired resolution with a dedicated cv2.VideoCapture, and then recreate rovGuiMainFrame.cameraCapture.