Mass update: rev 2fefa47 in devel contains "super" branch

[Edward K. Ream]

This completes #1169. The code is much simpler than before.

#1170 discusses a large number of pylint-inspired changes made in the "super" branch, and the risks involved. Imo, removing python 2 related cruft must be done now, no matter what the short-term pain may be.

The new code will form the basis of the "unity" branch. See #1171, which recommends retiring Leo's old look and feel. Imo this work is the best way to simplify Leo. We will all have a chance to vet this branch before merging it into devel.

I apologize in advance for any problems these changes may cause.

Edward