Introducing 'unique' property on fields. Making 'username' and 'email' fields unique on user type. Fixes #200.
Allowing 'element' property on field types to be a function, so we can have different elements based on field settings.
Changing 'text' fields with 'options' property to use the 'select' element.
Adding missing 'reference' field type.
Merge branch 'dev' into fs/taller-html5mode
Added updated attribute to verify when a type has been updated