fixing IE8 bug: popup "widgets can't be created without a uniqueId" on dashboard
refs #3530 page overlay

 * when the referrer is matched to determine whether the session should be started, don't match the domain. this caused trouble for some users and doesn't provide real advantages.
 * new method tracker.setApiUrl() that can be used if the tracker url and the api url (which is used in overlay) differ
copyright assignment in absence of Piwik legal entity