Implements a nifty `config` reader

This action is designed to facilitate scripting
lineman based on its configuration.

The first bit of usefulness will be to verify 
Sass is enabled before we go about installing
the bundler & sass gems in our heroku build path.
One can do that like this:

```
$ lineman config enableSass
false
```

This config will follow '.' properties in the app
config, and will even follow indexed subscripts 
(e.g. 'foo[1]')

```
$ lineman config watch.pages.files[1]
app/templates/homepage.us
```

Neat-o! cc/@jasonkarns @davemo @theotherzach