Code styling consistency

[anilyil]

Description of feature

Most of ADflow is in camelCase, but it is not completely consistent. I personally don't prefer using camelCase for all variables since it makes it difficult to read in my opinion. I also am not sure if this is consistent with pep8.

In #231 I introduced some changes that uses an underscore based naming change. I changed all my changes to camelCase in the python changes but left the fortran changes as is for now. Creating this issue so we can further discuss with @eirikurj.