Test of gg lensing for different lens properties

[chihway]

This issue is for developing tests to understand how well the gg lensing signal changes as a function of lens properties (stellar mass, luminosity, colors etc.).

A few references that are worth exploring:

• SDSS: https://arxiv.org/abs/astro-ph/0511164
• CFHTLenS: https://arxiv.org/pdf/1304.4265.pdf
• COSMOS: https://arxiv.org/pdf/1104.0928.pdf

This would be similar to this earlier test: https://github.com/LSSTDESC/descqa/blob/master/descqa/DeltaSigmaTest.py#L51, but we like it to be more general...

1. modify the sample selections (and move them from code to the config file so they can be changed easily)
2. make sure the test would run on different catalogs (buzzard, protoDC2, cosmoDC2; though for now cosmoDC2 does not have shear yet)
3. make sure the code can read in different validation datasets