Add area correction to get_data

[samaloney]

Add code to use pixel masks to create appropriate area norms. Very basic code can be extracted and improved

stixpy/stixpy/calibration/visibility.py

Lines 244 to 245 in fb3004c

	pixel_areas = STIX_INSTRUMENT.pixel_config["Area"].to("cm2")
	areas = pixel_areas[idx_pix].reshape(-1, 4).sum(axis=0)