Report network statistics

[Serchinastico]

We need to report stats related to the usage of the network in the host application.
The Android app is now recording how many bytes are being downloaded and uploaded.

In the API report, the parent object is called network and it contains just two values: bytesUploaded and bytesDownloaded expressed as a long.

[Serchinastico]

Update on this issue: we can't know for sure how many bytes the host app has downloaded/uploaded, we only have access to general stats, independent of processes. It's true that iOS is known for killing apps that are in background but...

Pending to take a decision on this.

[Serchinastico]

After a brief discussion with pedro, we agreed on applying swizzling to NSURLSession, we'd probably miss data streaming or webviews traffic but it's ok