Categorical docstrings referring to "Contingency Table tutorial", which has since been renamed

[Steph-Chong]

(1) Some categorical API docstrings refer to the "Contingency Table tutorial." This tutorial was renamed, and is no longer called "Contingency Table tutorial." The docstrings should be updated.
UPDATE: Has been resolved by PR #742.

(2) While I am not advocating renaming the tutorial file name (that will break too many links), I also wonder if the tutorial header and how it appears in the tutorial gallery/the left hand side bar of readthedocs should change. I wonder if it should be something more along the lines of "Binary Categorical (Contingency Table) Scores". Or perhaps "Binary Contingency Table (Confusion Matrix) Metrics" or "Binary Categorical Scores and Contingency Tables (Confusion Matrices)"?
UPDATE: Resolved by PR #741 and PR #743.