Remodel times to use datatype properties rather than TimeInstant

[rjyounes]

Proposal by @mkumba. Documents attached.

gistTime-apptx.pptx
experimentsWithDateDatatypes.ttl.txt

[rjyounes]

Adding to July 2021 project in order to consider postponing release of 10.0.0 to include these changes.

[rjyounes]

See description of #470:

As currently constituted (v9.7), gist provides no way to assert a start or stop time directly. It all relies on the use of TimeInstant instances, which can be cumbersome, hard to mint in a standard fashion, and not always necessary.
We should provide a standard set of datatype properties with an xsd:dateTime range. Provisionally, this could be something like:

gist:atDateTime
     gist:occurAtDateTime
     gist:startAtDateTime
     gist:endAtDateTime
     gist:createAtDateTime
     gist:changeAtDateTime
     gist:lastModifyAtDateTime

If adopted, some class restrictions should be rewritten to include the use of these in addition to the TimeInstant-dependent properties.

[rjyounes]

In the scope of this proposal, consider all issues labeled topic: dates and times.

[rjyounes]

See Dave's slides attached to the description for the implementation details. A couple of predicate name changes:

• XHumanInstant predicates change to XMinute - e.g., actualStartHumanDateTime => actualStartMinute
• XSytemTime predicates change to XMicrosecond - e.g., actualStartSystemTime => actualStartMicrosecond

Also consider the new predicate names in version 10.0.0 - see issue #188 and PR #535 where relevant.