Split up plots.py
Created by: Zaharid
plots.py became a lump of unrelated functionality that was getting very difficult to understand and navigated. We split it in two:
- pdfplots.py for things related to PDF plotting only.
- dataplots.py for things involving data in some way.
Only one one-liner utility function, _scale_from_grid overlaps between the two, and it has been moved to utils.py, used to guess the appropriate scale (as in linear or log).
Closes #227 (closed).