ENH: add progress bar to clustering stats

Addresses #1480

cc @Eric89GXL 
@Eric89GXL looks like this:

```
Found 1 clusters
[..........                              ] 25.00000 \    [Parallel(n_jobs=2)]: Done   1 out of   2 | elapsed:    0.3s remaining:    0.3s
[........................................] 100.00000 \    [Parallel(n_jobs=2)]: Done   2 out of   2 | elapsed:    1.6s finished
```