Have @since tag reflect component versioning

The current @since tag versions refer to Wikibase. The commit sets every @since tag to 0.3
since in version 0.3 of WikibaseDataModelJavaScript, all components have been moved from the
main wikibase namespace to wikibase.datamodel (see pull request #8). Obsolete tags are removed.
Consolidated Reference
Added generic init.php
Reflect actual main contributors
Removed Property.prototype.equals

Property.prototype.equals tries calling Entity.prototype.equals which does not exist anymore
since it was removed in pull request #7. Regardless of the need to re-implement
Entity.prototype.equals, Property.prototype.equals is obsolete code currently.
Merge pull request #15 from wmde/refactoring

General consolidations