we created the IEventSummary richttext behavior in plone.app.event because plone.app.dexterity was lacking a generic richttext behavior.
now work is done in plone.app.contenttypes to provide such an behavior.
When it's ready, we can just remove our IEventSummary behavior, use plone.app.contenttypes one (in the p.a.c Event FTI config) and write migration steps for that.
Refs #140 remove the IEventSummary behavior, since we now use p.a.con…
…tenttypes' IRichText behavior
Remove the IEventSummary behavior and use the generic IRichText from …
…plone.app.contenttypes instead. Fixes #140, Closes #142.