Support widgets

[jqnatividad]

Leverage new widgets capability.

We need not over-engineer this, just have a field in the Resource View form to add a JSON configuration file, instead of dynamically creating a form based on the schema of the table.

[jqnatividad]

See https://github.com/jqnatividad/cartodb15-workshop for AirBnB explorer example.

Check TUTORIAL for more info.