Added Cube.collect_dependencies() and Cube.distilled_hierarchies()
Added Cube.collect_dependencies() and Cube.distilled_hierarchies()

The Cube.collect_dependencies() is for attribute expression support
(see docstring for more info) and the distilled_hierarchies is a
direction into top-level hierarchies in Cube and to have SQL low level
backend objects Cube-free (better testing, maintainability, less
complexity. At least for now.).

jell0720/cubes,ubreddy/cubes,noyeitan/cubes,pombredanne/cubes,noyeitan/cubes,cesarmarinhorj/cubes,noyeitan/cubes,cesarmarinhorj/cubes,ubreddy/cubes,cesarmarinhorj/cubes,pombredanne/cubes,zejn/cubes,ubreddy/cubes,zejn/cubes,jell0720/cubes,jell0720/cubes,zejn/cubes,pombredanne/cubes