Enable event feature on MongoDB and DB2

This bp aims to implement the event feature on Mongodb and DB2

The basic structure of Events on Mongodb and DB2:

model of db:
- events
    - _id: uuid of event (Event.message_id)
    - event_type: description of event's type
    - timestamp: time stamp of event generation
    - traits: [array of {trait_name: string, trait_type: integer,
              trait_value: data}]

Structure that is proposed will support next queries:
- timestamp of events generation
- event id
- event type
- trait: trait_field, type(int,string,etc.), trait_value