Remove references to ISO8601 in all date/dateTime properties

[siuc-nate]

ceterms:endTime has the following usage note (Curiously, ceterms:startTime does not):
"Start and end dates and times of the credentialing action (in ISO 8601 date format). For actions that span a period of time, when the action ended."

This usage note should be removed, or at least, the reference to ISO 8601 should be dropped, as the xsd:date is more restrictive than the ISO8601 date - namely in that it requires a full date rather than allowing a partial date.

For the same reason, the definition of ceterms:temporalCoverage should be updated from:
"The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes, either as a DateTime or as a textual string indicating a time period in ISO 8601 time interval format."
to:
"The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes."

[siuc-nate]

Actions to be taken:

Remove

Subject: ceterms:endTime
Predicate: vann:usageNote
Object: "Start and end dates and times of the credentialing action (in ISO 8601 date format). For actions that span a period of time, when the action ended."

Remove

Subject: ceterms:temporalCoverage
Predicate: rdfs:comment
Object: "The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes, either as a DateTime or as a textual string indicating a time period in ISO 8601 time interval format."

Add

Subject: ceterms:temporalCoverage
Predicate: rdfs:comment
Object: "The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes."

Note: ceterms:spatialCoverage also (incorrectly) references ISO 8601, but that is to be handled in this issue: #372

[stuartasutton]

Nate, we need to look at all of the following properties so we aren't handling these date issues piecemeal:

ceterms:alignmentDate
ceterms:dateEffactive
ceterms:endTime*
ceterms:foundingDate
ceterms:startTime*

With the exception of endTime and startTime, all of these properties need their date range changed from xsd:dateTime to xsd:date.

In other words, we leave endTime and startTime with `xsd:dateTime.

We also need to add ceterms:endDate and ceterms:startDate with a range of xsd:date. Then, where we are currently using endTime and startTime, we should use endDate and startDate.

We currently have nothing that I can see that requires both the date and time...but we should not deprecate these date/time properties since they might be used in the future and we'd like to not have to add them back in after we've deprecated them.

I want to think more about removing references to ISO8601. The permissive breadth of the ISO standard does not mean it can't be referenced where a more constrained use is in operation.

[siuc-nate]

Thanks, Stuart. I have a separate issue setup for the date/dateTime range problem: #369

This issue is just about removing references to the ISO standard from the definitions/comments of CTDL properties as outlined above. I don't think it's necessary to include that reference anyway, as it conflicts with the definition provided by the xsd:date (and dateTime) ranges.

[siuc-nate]

Per our 4/7/2017 call:

Actions to be taken:

Remove

Subject: ceterms:endTime
Predicate: vann:usageNote
Object: "Start and end dates and times of the credentialing action (in ISO 8601 date format). For actions that span a period of time, when the action ended."

Remove

Subject: ceterms:temporalCoverage
Predicate: rdfs:comment
Object: "The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes, either as a DateTime or as a textual string indicating a time period in ISO 8601 time interval format."

Add

Subject: ceterms:temporalCoverage
Predicate: rdfs:comment
Object: "The temporalCoverage of a CreativeWork indicates the period that the content applies to, i.e. that it describes."

[siuc-nate]

These changes have been made in pending CTDL and noted in history tracking.