Prevent the plots from being cropped

[nathanncohen]

The problem is that the scatter command which is used to draw the circles does not impact the area plotted : one can draw things outside of what appears on the picture. If one instead uses the circle command, there is no guarantee about the size of the text compared to the size of the ball. A correct way out may be given in the following thread (second answer)

http://www.mail-archive.com/matplotlib-users@lists.sourceforge.net/msg19663.html

CC: @rlmill @sagetrac-mvngu @jasongrout

Component: graph theory

Issue created by migration from https://trac.sagemath.org/ticket/10531