Add autofill support

[mbahgatTech]

To-Do

• Add support for auto-filling some fields based on the values of other fields.
• Potentially disable editing for these fields.
• Abstract the functionality for it to be specified in fields.json.

Potential fields.json format:

{
     ....fieldStuff,
     autoFill: {
          depenencies: [
               "field name", 
               "field 2 name"
          ],
          "arguments": "dependencies",
          "body": "return dependencies[0] * dependencies[1];"
     }
}