pySim.log, pySim-shell: fix compatibility with cmd2 >= 3.0.0
Some Linux distributions (e.g. Arch Linux) already ship cmd2 3.x.x,
which removed the style()/Fg/Bg API in favor of stylize()/Color.
Add a version guard to select the right API at runtime.
Adjust the upper bound cap in requirements.txt and setup.py.
Change-Id: Ibf2ac7847933296fb06665c87f53ed6e1f315d27
