Properly implement GPL license

Few minor, mostly technical changes here which serve simply to clarify the copyright and license as (I believe) originally intended:

* License as GPLv2 or later to allow GPLv3 compatibility (WordPress recomended best practice)
* Explicitly included GPL header in main plugin file (per GNU's implementation guidance)
* Explicitly state Storify's copyright and year of publication
* Proper PHPDoc copyright and author license headers
* Remove my name which was erroneously included as a result of a template default
* (Automatic whitespace cleanup on lines 1000+)

Again, there are no code changes here, and this pull request should simple serve to reduce copyright and license ambiguity, and is not intended to modify any existing rights.