Analysis class

[philippeller]

Current analysis class is overly complicated with 2k+ SLOCs and nested function calls that I cannot really see through....
Simpler >> Complicated

[JanWeldert]

Adding to this, the analysis.py script is also much too long with more than 3.5 k lines. Since it contains multiple classes and helper functions, splitting it up in different files (all located in pisa/analysis) should not be too difficult.