Separate Container like behavior from "aq_column_block" into a more flexible "block-container" for better extendability.

I really need this kind of functionality for the theme that I'm working on currently. Of course I could try to hack around and write my own JavaScript, but I think that everyone could benefit from a little more modular approach.

I think that this commit is only the bare-bones of what could be possible, but I think it's going to do just fine for now. 

I would really love to see this included in the public plugin so that I shouldn't pack my theme manually with it. In any case, any feedback is very much appreciated.

Cheers,
Norris.