Changes to Extension Template

[jyutzler]

As noted in #160, the extension template should not have been declared normative without approval from the OGC document committee.
In addition, the extension template lacks a place for an Abstract Test Suite. Now that we are doing #132 this matters because it makes no sense to present an ATS for extensions that have not even appeared in the document yet.
The same applies to Table Definition SQL and trigger SQL.