Ensure profile loading doesn't break on partial profiles

[nicholascar]

If a prof:Profile appears in data without certain properties, Prez crashes as the profile loading queries break. This may occur when a prof:Profile object appears in data that is not intended to be a Profile understood by Prez, e.g. a background ontology used for property labelling that just happens to be a prof:Profile (like the IDN's DCAT Profile).

Ensure that the profile loading functions do not load partial Profiles and doesn't crash.

[recalcitrantsupplant]

We could subclass profiles intended for use with prez as prez:Profile's and look for these instead. Thoughts?

[recalcitrantsupplant]

@nicholascar could you if this is still an issue