Add cleanup function to remove unnecessary fields from schemas

[miguelgrc]

Add a function to be run likely after every change in the schemas that removes unnecessary fields (i.e. fields with default values like "ui:label": true) so that we don't pollute the schemas with useless information. This can be done by iterating through the schemas in a smart and efficient way and check the jsonschema specification and/or a custom defaults object to discard those values that are unnecessary.