Add ability to read Compass directory and filenames

I'm working for Liferay.com and our lead engineer, Ray Auge, spoke with Joonas Lehtinen about this feature. As Liferay needs this functionality for its Portal CE project, Joonas Lehtinen mentioned that we could contribute to the VAADIN project. 

My design was to use the stylesheets here:  https://github.com/chriseppstein/compass/tree/stable/frameworks/compass/stylesheets and modify the VAADIN code to be able to read them in such that our existing Ruby implementation can be replaced with VAADIN without any changes to our *.scss and *.css files.

As this is a bit of effort, it may take several pull requests to complete. 
This, then, is the first of several commits toward this effort.