Make python 2 and python 3 bindings not conflict

It would be great if the python 2 and python 3 bindings of vtk could be installed at the same time without conflicting. Currently, most libraries have the python version number embedded in their name, which allows them to live side-by-side without conflicting. However, a few do not, which makes it impossible to have both bindings in the same prefix at the same time. This is particularly important for Linux packaging, where supporting both python 2 and python 3 at the same time is preferred.