Add better method for supplying not-yet-created handlers

[wagnerrp]

The Datapoint definition allows a handler callable to be supplied, for which the data returned by queries is passed through. Due to the manner datapoints are defined, and Python's lack of prototypes, this handler must be fully defined in the namespace at the point the Datapoint is created. This leads to circular dependency issues where two classes must be defined before each other, such as the Studio class having a 'parent' attribute that back-references to itself during its own creation. Right now, this is worked around by using a lambda function, however that prevents the locale passthrough from happening properly.