Send a message if there is a large deviation in ticker mentions

[StephanAkkerman]

If $LUNA gets mentioned a lot, whereas this often would not be the case. Then send a message.

• [ ] Database with the (rolling average) amount of times a ticker is mentioned
• [ ] Compare number of times this ticker was mentioned today with the db

For how long do we store the tickers? Maybe a month max What do we consider a large deviation? We could calculate the daily std and compare it How do we handle new tickers? Maybe minimum 7 days of data

[StephanAkkerman]

Do this after #524

[StephanAkkerman]

We should also consider the amount of unique users that mention the ticker (otherwise 1 user could just spam the timeline by tweeting and retweeting)