Add more support for config items in front and backend

[jlec]

• copy acl and tcp-request support from front to backend
• Introduce _extraconfig as a free form config list

[benwebber]

Thanks for contributing, Justin! Would you please:

1. merge master into your branch to pick up the backend ACLs from #89,
2. add extra_config to the other top-level configuration groups as well?

Thanks!

[jlec]

The whole thing can be improved. Let me rework this and submit another PR