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
Stub for clean() method to validate fields

to be filled TODOs by newbies
Refactoring: split models in subfiles

Import them as usual!! like: from base.models import modelname
Merge branch 'master' into tapion