Comment time not showing in structured data testing tool, itemtype Organization added

* Bugfix: added time-tag to comment date, moved itemprop=commenttime into time-tag, changed comment datetime function to comment_time('c') to add time zone offset
* normalised Changelog.txt, straightened semantics (replacing "object" with "item")
* Enhancement: added itemtype Organization with properties: url, logo, name, description to header.php
* Enhancement: Organization name and description can be entered from theme options, if left empty values from blog will be used; added two new functions, piratenkleider_tag_schema_org_desc and piratenkleider_tag_schema_org_name, to functions.php