Added first API definition
Untested model compliant to specifications

IMPORTANT:

* Split Event from EventHappening that bounds an event to one
  or more timeslots
* Added EventPerson to bound people (animators) to events

and...

* Tried to be compliant with "Dominio" document
  - s/ScoutGroup/Unit
  - s/SubCamp/District
* Person model to holds people related to events