Removal of hierarchical class structure: New API structure

[picciama]

Is your feature request related to a problem? Please describe.

The hierarchical class structure of oktoberfest does not allow execution of individual functions within the pipeline out of the box. This makes bugfixing, investigation and enhancement difficult.
Plus, it is not the most userfriendly way we could do this and it is difficult to extend the existing code base.

Describe the solution you would like
Removal of the hierarchical class structure, that is basically only there to have shared access to the spectral library object.
Instead, a linear API, that executes static functions that return the spectral library object after modifying it.
In addition, high level functions that execute all of these functions to keep the current way of executing oktoberfest.

Tasks:

• come up with a structure of functions
• check where and how submodules should be organised
• cleanup the code

Additional context
Making oktoberfest code base cleaner, future proof and lightweight