Adding sample checking module, Telescope data parser

Hmm, the problem is that if we take out this check here, we have to maintain counts per metric. Otherwise if the caller doesn't know they have to only pass in download_throughput, the results for all metrics get added together, which we don't want.

Then we have the issue that when the caller calls `blacklister.is_blacklisted('lga01-comcast-upload_throughput...')` something in the stack has to do something like:

```
# Workaround until Observatory supports omitting datasets on a per-metric basis
if metadata['metric_name' != 'download_throughput':
  metatadata['metric_name'] = `download_throughput`
```

Actually, now that I write that out, it doesn't seem so bad. The hacky workaround stuff could be contained at a high level in `DataFileBlacklister` rather than way down in `SampleCounter`. I'll do it!