Measure latency of HTTP requests.
Limit foreign relation tests to CommonData ones.
Implement time correction from HTTP date field.
Apply correction to Android notification.
Merge pull request #277 from toggl/roosmaa-time-correction

Correct phone time based on server time.

With every HTTP request we receive the Date header, from which we can determine local clock offset to proper UTC time. We hook this information into the ITimeProvider and now our app is always displaying the correct time regardless of the users phone time settings.

We use the median value of the last 21 measurements to determine the effective correction that the whole app uses.

Closes #25.