Pin mininet/... version

[oliviertilmans]

The current setup.py script lists dependencies, but not their version.

It would make sense to explicitly pin the version used by ipmininet to ensure that future updates don't break things...

Out of all the dependencies, I think we should:

• Pin mininet to an exact version
• restrict mako to a major version
• specify a minimum version for everything else

Is mininet even on pypi at all? If not, we can add in the setup script how to install the particular version we require (so that issuing 'setup.py install' is the one-liner to get ipmininet running)