Make cosmology a free parameter

Notes

changing the FlatLambdaCDM to be able to take all cosmologies that are available in astropy cosmology
inputs for the cosmologies are actually coming from the yaml. Want to define the distribution same as others.
Want to be able to set the cosmology parameters as distributions as well. (Look at example yaml with distribution categories)
Cosmology variable info would need to be done dynamically

deepskies / deeplenstronomy