Add custom fields from autoload (psr-0)

I could not get the current way of adding custom fields to work with my application that auto loaded the field classes with psr-0. It would usually complain that it could not re declare the class or fail to work entirely.

Anyway this PR allows the "type" field to define the class name by adding one more parameter called "namespace". Like so

`<field 
                name="bio" 
                class="form-control" 
                type="\Modules\Media\Field\Editor" 
                namespace="true"
                label="Bio" 
                />`

This could probably get added in a better way, but for my uses this is fine. Call this a feature request with an example. I am willing to put more time into making it better if anyone has any ideas for it.