Refactoring, following Pylint

[evertrol]

Pylint still leaves some suggestions, which are swept under the rug by use of command line flags disabling them:

• reduce amount of local variables (too-many-locals)
• reduce amount of branches (too-many-branches)
• reduce amount of arguments (too-many-arguments)
• reduce amount of statements (too-many-statements)
• replace or expand classes (too-few-public-methods)
• reduce duplicate code (duplicate-code)
• use consistent names (not a Pylint warning)

Notes:

• for some functions, it may be useful to have all arguments spelled out, instead of having a Matplotlib-like solution with **kwargs. A config dict could be an alternative, but this is less clear as well (and basically the same as just `**kwargs``).
• classes with too few public methods were created to allow multi-parameter functions be used in multiprocessing, using the __call__ method of classes. functools.partial could replace this.
• consistent names concerns options/arguments/variables such as reference_period vs control_period.