plone.app.event integration

integration of plone.app.event by providing an FTI profile for Event using plone.app.event's Dexterity behaviors.
Fixed tests.
Missing: migrations.
Note: currently needs source checkouts for plone.app.event (needs version > current version 1.0rc3) and plone.formwidget.datetime (needs version > current version 1.0b6).