The semantics of property paths are now:
(1) if a property path is set, it is _always_ respected (relative to the object
of the parent field)
(2) if no property path is set, the object of the parent field is _always_ ignored
Fact (2) allows us to set data into fields that is updated independently of the parent
field (like CSRF tokens, subforms with different objects etc.)
What is missing now is support for subfields that pass the object of the parent field
through to their own subfields. This functionality would be needed for GoogleMapFields,
DateRangeFields etc., which are compositions of individual fields that update the
parent object of the FieldGroup.
There are several alternatives for the latter functionality that should be discussed
in a RFC.
Fields can now easier support different data types in their underlying object.
These datatypes can be normalized to a single datatype using a normalization
transformer. The normalized value can then be transformed to the user's
representation with the value transformer (better name required?).
Property paths such as fields[group].fields[innerGroup].data were not being resolved correctly, since the second iteration of addError() (based on "group") would attempt to call get('fields') instead of get('innerGroup'). Solution is to remember to bump the propertyPath forward if we're at the fields property
