Feature/hot topic of the day

This feature is a script to calculate the hottest `tokens` of the day. I works by adding up the freqdists of every article published on a given day. It's different than whats is shown in the Media cloud dashboard (number of articles mentioning the word), here we calculate number of times the word has been printed on a given day.

It's not done yet, but I'd appreciate some input. The Idea is that we create a collection with these global freqdists in Mongo so that we can easily extract time series  for analyses.

==== THIS REQUIRES THAT THE ARTICLE COLLECTION HAS BEEN SENT TO PYPLN ====