TODO
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* handle selection and multiple selection property types
* handle date property type
* handle tokens property type
* handle boolean field
* make lines property type work
* disable deletion checkbox for non-deletable properties
* disable value field for non-editable properties
* add tests
* improve docs in README.txt as well as describe how form works in a form
  description, specifically on how selection property types work; improve
  installation docs re z3c.form versions and installing Plone z3cform support
  via quickinstaller
* test on plone4
