More CUDA optimization / minor restructuring

The remaining difference in performance between tHogbomCleanHemi and tHogbomCleanCuda seemed to be that the hemi version pre-allocates its storage in the class constructor, so I updated tHogbomCleanCuda to do the same.

New performance (on K40, this time with ECC off):

    Time 1.1 (s)
    Time per cycle 1.1 (ms)
    Cleaning rate  909.091 (iterations per second)