Enhancement: Add support for checkbox input

[saicheck2233]

Description: Add support for checkbox inputs, below is the schema used for generating a checkbox. format:checkbox and enum is needed for generating checkboxes.

{
    "$schema": "http://json-schema.org/draft-03/schema#",
    "type": "object",
    "properties": {
        "radio1": {
            "type": "boolean",
            "format": "checkbox",
            "title": "Animal",
            "required": true,
            "enum": [
                "Dog",
                "Cat",
                "Bird"
            ]
        }
    }
}

Changes:

Schema needed to generate a form with checkboxes.

Generated form with checkboxes.