Changes

setup.py: Align cmd2 minimum version with requirements.txt

As pointed out in the commit-log of Change-Id
I5186f242dbc1b770e3ab8cdca7f27d2a1029fff6 we had different minimum
versions for cmd2 in requirements.txt vs setup.py.  Let's align that.

Change-Id: I71cee0ec3ed2abec68ec567beaab13c868721dad

pySim-shell: drop backwards compat quirks for cmd2 < 2.6.2

Remove version guards for cmd2 < 2.0.0 and < 2.3.0, the Cmd2Compat
and Settable2Compat wrapper classes, and the old fg/bg color API -
none of these are needed since both requirements.txt and setup.py
already mandate cmd2 >= 2.6.2.

Change-Id: Ifd1c484ab66d74323d10e946347daa637cf6f5d8

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