Errata in non-normative SSNX and Dolce-Ultralite alignment modules: PR#1000

Dear all,

Following our discussion today, I updated PR#1000 as follows:

 - implemented the changes in the spec (html document): sections 6.1, 6.2,
and appendix D (changes)
 - added a comment to the pull request to suggest some text to add to the
Errata document.

See https://github.com/w3c/sdw/pull/1000 for more details.

Best,
Maxime