Improved custom forms

I've been working with foundation for over a year now and one piece has consistently caused frustration. I decided to take the time to work it over and propose some changes.

## Resolved Issues

1. Toggling doesn't work properly. When clicking on a `div.custom.dropdown.open a.current` or `div.custom.dropdown.open a.selector` the `.open` class should be removed, but it's not.
2. The height / sizing of dropdowns does not align with regular inputs which makes it almost as inconsistent as using normal `select` elements.
3. The default behavior of width / dropdown div is weird, from the fixed width on the dropdown `ul` to the javascript specified width of default elements. It would be best practice in my opinion to make the select behave in the same way as regular inputs by default so that you can implement them in a form easily.
4. When an option overflows the default width, the dropdown `ul` should expand further than the `a.current` element. Similar to the way dropdowns usually work.

## Unresolved Issues

* It seems like it would be good to position the dropdown element *above* the div when near the bottom of a page.
* It seems that customizing and styling the dropdown should be easier. Possibly with a boilerplate customization file or something to work with, or more settings.

I'm attaching a screenshot of what my changes look like. I'm sure there's a lot of things I'm missing with this pull request. Also, I expect that some of my changes could very well be considered breaking changes. But I'd like to open this conversation and work on this with everybody until we can get a solid makeover in place for these dropdowns.

## The New Look
![Screen Shot 2013-02-13 at 6 36 50 PM](https://f.cloud.github.com/assets/687594/155420/b94d5e9e-7647-11e2-9161-4f559fed88b2.png)