Replacing keyword arguments in single_event/likelihood.py

[kazewong]

#172 @maxisi @tsunhopang

Is your feature request related to a problem? Please describe.
As of the version of jim in #172, the likelihood class takes a general set of kwargs in its constructor. This is not ideal because it makes the diagnosing problems and bookkeeping harder.

Describe the solution you'd like
We should remove the use of kwargs in the likelihood class. However, one complication is currently the likelihood class calls a likelihood helper function as shown in

jim/src/jimgw/single_event/likelihood.py

Line 668 in bb0dee3

def original_likelihood(

, and these likelihood helper functions have a varying number of arguments.

I think a solution can be instead of the current inheritance hierarchy, we either separate out the marginalization schemes into their own classes. However, that extra specification of kwargs are then just propagated one level up. At some point there is a design choice regarding where should the kwargs be specified, ideally in some json/yaml file