py-complete--base: `py-shell-complete-intern' backend disabled

use `py-shell--do-completion-at-point'
Move menu simplified. Display a limited choice at once only. 

"More"- button added
Redundant command `py-send-region-and-go' removed

This is provided already by `py-execute-region-switch'
Unused `py-dot-word-before-point' removed
py-docstring-style pep-257-nn closing quotes, lp:1241147, fixed