Include common configurations in separate module

[jonschipp]

Don't clutter the ContainNSM repo, keep it simple. Configs, rules, and other user contributions should be in a separate repo called maybe containnsm-extra or containnsm-contrib or w/e. This will contain things like rules and configs for snort and suricata to make it easier to use the tools.

I think including it via a git submodule will do the job. If they user wants it they will have to clone with git clone --recursive ... to retrieve both the ContainNSM and extra repo. I'm open to other suggestions.

[jonschipp]

Specific options for snort, etc. containers can be handled in run_options() of containnsm. For example, directory containing snort rules and config would already mount in appropriate place once the snort image is tested to have been passed as an argument. Not sure how to handle selecting different versions of rules though - that might be tricky. Simple to do -v <rules_dir>:<rules_dir> for the latest though