Added object title in JSON schema

[discharged-spider]

Added class name as object title in json schema. Really useful when creating forms from schema (especially in lists).

[beregond]

Hey, @discharged-spider - nice small feature. :) This pr still needs to fix tests, and maybe to develop extra option to define other name than type.__name__ - like type.schema_name (which can be property that returns type.__name__ by default).