Add size policy to base widget

- Create a DimensionPolicy psuedo-enum containing the possible values
  for resizing policies of a specific dimension of a widget
- Create a SizePolicy "class" to contain a widgets desired sizing info
- Add a sizePolicy property to the BaseWidget "class"
- Add foundation meteorite package
Add min, max, and preferred size to BaseWidget

- Add Size class to Widget module for storing height and width of a
  widget (I wonder if anything other than a widget will ever need
  a size?)
- Add properties to BaseWidget for min, max, and preferred size
Begin conversion to new widget rendering system

- Add "size" property to BaseWidget for storing actual size of widget
  - This property will be set during the measurement phase of the
    rendering process, but until that's implemented, each widget sets
    it's size manually in it's constructor
- Set a default SizePolicy in the BaseWidget constructor, and have each
  widget make a "super()" call in their constructors
- Convert each widget's render() method to return a jQuery element
  instead of an html string, for cleaner manipulation of the DOM
  - Also convert document.js -- which will likely be converted into a
    widget itself -- to accept these new jQuery elements while rendering
    the notebook ("document")
Add stubs for api and collections api