Run THELI on shapepipe part 1

[lbaumo]

Summary

• adds a bash script to convert THELI output to shapepipe input
• changes bookkeeping in get exposures module
• merge headers module now accepts external scamp headers
• wcs no longer switches from PV to SIP, keywords are automatically changed in split exposure module, closes issue Remove the SIP to PV conversion #612
• no longer explicitly sets weights to 1 after rescaling during shape measurement

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[martinkilbinger]

Add the label for the PR. Otherwise looks good.

[martinkilbinger]

Please set the label of the PR.

[aguinot]

This will create an issue. Line 859 there is weight_map *= 1 / sig_noise ** 2 if the weight_map is not equal to 1 it will lead to weird behavior.

[lbaumo]

for theli weights, there are relative weights between pixels, which then need to be rescaled by the sky background variance to become variance maps. Thomas Erban seemed to think this operation was okay. are you talking about the weirdness associated with some megaprime weight maps that are not always 1 or 0?