Refactors Security Groups into their own module

Pulls security groups and their associated unit tests into separate
submodules intended to make plugin.py easier to read.
Moves IP Policies into their own plugin module

Refactors plugin.py, moving IP policies and associated tests into their
own modules for enchanced plugin.py readability.
Merge pull request #134 from Cerberus98/ip_policies_submod

Ip policies submod