Base form issue

[Jtplouffe]

There seems to be an issue when having multiple forms extending a common base form.

Let's say we have the following base form:

export class BaseForm {
    @Control()
    public name: string;
}

And the following children forms:

export class ChildFormA extends BaseForm {}

export class ChildFormD extends BaseForm {
    @Control()
    public description: string;
}

When instantiating the ChildFormA form, one of the children in the _model array in the FormGroup will be undefined.
I think it's an issue with decorators applying / reading the metadata to the base class instead of the child class.