Add a global option to to skip hierarchical processing for facets so they are rendered as "flat"

Some display widgets don't lend themselves well to hierarchical facets. For example, the Tagcloud Facets and Chart Facets modules wouldn't make sense with facets whose hierarchies are processed because all of the children facets are hidden by default. Therefore facets will suddenly appear when parents are activated giving the end user no clue as to why they appeared.