Copulogram

This release:
- Fully redesigns the Copulogram class by moving from the seaborn PairGrid object to a matplotlib subplot. This major modification provides more flexibility to tune axes display.
- Drops the interactive Copulogram method to simplify the class. This action allows removing the Bokeh requirement.

This release:
- Fixes window scaling of the upper triangle in the copulogram
- Adds an example plotting an input-output copulogram of the Ishigami function.