New Feature: Support command objects with maps of complex objects

1. Create command object class

```
class SaveProductsCmd {

Map products

}
```
1. Create action with command object `SaveProductsCmd`
2. Send post request to action with data.

Expectation - product objects in map:

`cmd.products == ["a": new Product(...), "b": new Product(...)]`

Reality - maps in map:

`cmd.products == ["a": [title: ...], "b": [title: ...]]`

Start by locating the command-object binding path used by the action described here, then reproduce the POST with a SaveProductsCmd containing a Map. The work is done when cmd.products contains Product instances keyed by the submitted map keys rather than nested maps.

Written by the indexing model from the issue text.