STEREO JPEG 2000 headers to store previous CRVAL values

[Jack Ireland]

Currently, the STEREO branch of JP2Gen recalculates CRPIXn and sets CRVALn to zero. These original values should be stored as an explicit HV_ tag, something like

HV_CRVAL1_ORIGINAL

This makes the original positioning information much easier obtain. Also, a flag should be included to say if HV_RECALCULATE_CRPIX was called or not.

[Jack Ireland (jack-ireland)]

This should be extended to include the original versions of CRPIX1 and CRPIX2.

[Jack Ireland (jack-ireland)]

This bug also leads to an improvement to the STEREO JPEG 2000 headers that we should probably implement:

(1) replace the existing JPEG 2000 headers with an exact copy of the STEREO FITS headers
(2) New positioning information is included as Helioviewer keywords.
(3) Helioviewer clients are re-coded to look for those Helioviewer keywords in the case of STEREO data.

This maintains the fidelity of the FITS header in the JPEG 2000 header, and allows us to store Helioviewer-required positional information in the JPEG 2000 header separately.

[Jack Ireland (jack-ireland)]

STEREO data from 2006 onwards - with this fix implemented - is being written and transferred to Helioviewer.