New test for high scale to get tweet

New test, called "TweetScalerSpec", which retrieve a large
amount of tweets from twitter (300 parallel queries) and check
for duplicates, while computing local counts.

The system is design for long-term runs.
Fix bugs in TweetManager, now works in scaled test

The way the calculation of the update rate was handled was wrong.
It is now corrected and should be working. Addition of a test, launching
300 TweetSearcher, which works.