Progress on a polygonal modeler.
New Modeling Kernel ------------------- This commit adds a new modeling kernel based on [Boost.polygon](http://www.boost.org/doc/libs/1_58_0/libs/polygon/doc/index.htm). It currently supports a very limited set of operations: + Creation a model. + Creation of model vertices. + Creation of model edges. Internally, an edge split operation is provided but not yet exposed. Miscellany ---------- + Fix a bug in attribute association. Because model entity items in attributes may have a membership mask, calling `setValue()` does not guarantee that the association will occur. Return the proper boolean or infinite recursion will occur inside `Attribute::associateEntity()`. + Add a Python-callable variant of ImportJSON::ofLog. + Have `smtk.simple` hang on to operator results so that scripts can access them if they need to. + Fix error log printout in `smtk.simple` API. + Have python test `addToScene()` method return pipeline objects.