Update provenance terms to be consistent with NIDM style

Couple updates to use similar standards as NIDM for class names and attributes in provenance documents.

- [X] Use capitalized CamelCase with class names
- [x] Use lowercase camelCase with attribute names (in the nipype ns) 
- [x] Include [interface class name](https://github.com/nipy/nipype/blob/master/nipype/utils/provenance.py#L261) as an prov:type (?)