Remove SHACL terms for DL compliance

[rjyounes]

See discussions in #155 (closed), #389 (closed), #593 (same concerns apply as in the previous two issues, but this one has not been closed), and #934 (slated for next release).

We have discussed the issue of keeping gist strictly OWL 2 DL-compliant and each time come back to the conclusion that it should be. If we follow through on that we must remove the SHACL terms because they are not OWL classes and properties.

[rjyounes]

I am strongly in favor of removing these terms. It's high priority to be DL-compliant, IMO.

[sa-bpelakh]

Move prefix declaration to separate file, reference in editorialNote, solicit input from @Jamie-SA