Add estimated time remaining to progress bar
Add estimated time remaining to progress bar

This is what the output looks like while processing (that line updates)
```
Started at 2016-05-04 02:05:44
Processing [.............................                     ] 71/124 57% 0:00:16 remaining
```

And here's the final output:
```
Started at 2016-05-04 02:05:44
Processing [..................................................] 124/124 100% 0:00:00 remaining
Finished at 2016-05-04 02:06:21
Elapsed time: 0:00:37
```

qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq