Revert "Revert "don't construct sphere tree""
Revert "Revert "don't construct sphere tree""

This reverts commit d7382ef02f6e6f2beb2229e40aaf64fc5db00178.

joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue