modified history to use the mongo connection from the tweeters service instead of having a separate connection.  This way, connections are not leaked.  The TweeterHistory class is not as clean, but this version tolerates the page being refreshed without leaving lots of connections open.
merging changes before posting version that shares mongo connections

Merge branch 'master' of https://github.com/XDATA-Year-2/twitter-mention-history into shared_mongo_connection