Definition of  "objectModel"

**Terms**: `nidm:objectModel`, `nidm:NIDMObjectModel`, `nidm:FSLResults`, `nidm:SPMResults`
**Definition**: No definition yet...

This issue is open to discuss the definition of `objectModel` (attribute), `NIDMObjectModel` (range taken by `objectModel`) and `SPMResults` / `FSLResults` (sub-classes of `NIDMObjectModel`).

Example of use:
```
entity(niiri:spm_results_id,
    [prov:type = 'prov:Bundle',
    prov:label = "SPM Results",
    nidm:objectModel = 'nidm:SPMResults',
    nidm:version = "0.1.0"])
```

I am not sure about the naming of these terms. In particular, what is intended by "NIDM object models"? Are those the same as "NIDM components"? @satra I thought you might want to comment on this...

Any suggestion on the definitions or the naming is greatly appreciated.