@crccheck are you okay with this assignment (given the model rename to EmbedType)?

`obj.type` is clear and doesn't endanger the built-in. It also allows us to standardize references. ArmWells [does it](https://github.com/armstrong/armstrong.core.arm_wells/blob/06b81b4a1e9bd6fd2bdc7f1441277f8fdaa035cf/armstrong/core/arm_wells/models.py#L135) and we can take advantage with the new ArmLayout "by type" [mixin](https://github.com/armstrong/armstrong.core.arm_layout/blob/v1.3.0-prep/armstrong/core/arm_layout/mixins.py#L98).