Add gutters back into the D7 branch

Gutters were actually part of @chrisryan's original 7.x port at https://github.com/chrisryan/openadstream, but we felt that they were somewhat extraneous/secondary.

Our rationale for cutting them: the module was essentially trying to do what any decent themer should be able to do on their own. To "sandwich" an entire page with ads (per README.txt), the themer would really just need to define additional regions and assign blocks per. To us, maintaining a dedicated interface to control ad padding, background color, left/right positioning, DOM identifiers, etc. just seemed kinda bloated.

Happy to take a look at bringing it back if you feel like its definitely worth keeping.

I'd prefer to just handle gutter ad positioning/display in my theme. I can't imagine the module would be able to handle this without additional effort in most themes anyway. Plus, gutter ads seem like kind of an edge case these days. That's my 2¢.