Support static/class properties.

_From [k...@chromium.org](https://code.google.com/u/101260952816761938100/) on October 22, 2013 10:59:25_

Currently, all properties are stored as instance variables, but we need to add support for static/class properties.

This could be done by specifying the allocation-scope of the property as either instance (the default) or static. Everything would work exactly as it is now, except that static properties would be stored in a map named static_ stored in the prototype, instead of the instance_ map in the object itself.

_Original issue: http://code.google.com/p/foam-framework/issues/detail?id=26_