Allow for mutliple forms on a controller

Currently easyform will not allow for:

```
{{#each address in editableAddresses}}
   {{#form-for address}}
      {{input name}}
      {{input street}}
      ...
   {{/form-for}}
{{/each}}
```
as it always gets the form model from the context (which is the controller). It should use the passed in object/model when available.