Cc 5709 airtime analyzer cloud storage

Code review 1
Rather than having if($media->isInCloud()) in all these StoredFile functions, make a subclass of StoredFile called something like CloudStoredFile, and override the methods you want to change, calling the parent class functions where appropriate.
I think we should use "Class Table Inheritance" from Propel, which will also let us store any extra columns we need in a different table: http://propelorm.org/Propel/documentation/09-inheritance.html#class-table-inheritance