Provenance of provenance about a SPM Results model

This proposal is to include the version of NI-DM used when generating a document. Essentially this is allowing provenance of a provenance document, where the NI-DM model is contained within a `prov:bundle` and an extra entity is included at the top level of the document representing the bundle. For example:

```
document
entity(niiri:spm_results_id,
  [prov:type = 'prov:Bundle',
  prov:label = 'SPM Results',
  nidm:objectModel = nidm:SpmFmriResults,
  nidm:version = '0.1.0'])
wasGeneratedBy(niiri:spm_results_id, -, 2014-05-19T10:30:00)
bundle niiri:spm_results_id
  # actual model goes here
  ...
endBundle
endDocument
```

Additional information could be included, such as the Agent (SPM) that generated the document, and the Activity (ni-dm export function?), but wanted to keep it simple to start. Note that there are three new terms here:

1. nidm:objectModel - an attribute to indicate the type of model in the bundle
2. nidm:SpmFmriResults - the name of the model, should dereference to the specification
3. nidm:version - version of NI-DM the document conforms to per http://semver.org/

Warning: The [specification on bundles](https://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#component4) appears to support this, but currently throwing an error at provenance.ecs.soton.ac.uk. @satra am I missing something here?