Added downloadable content support
Refactoring
Workaround for non-consumables with downloadable content being restored twice (!?)
Added public property storeDownload and code refactoring.
Merge remote-tracking branch 'xgil78/downloadable_content_support' into download
Only start downloads if there is a least one
Fix tests
Backwards compatibility with iOS 5
Indicate availability
Sort members
Refactor download state methods
Refactor transaction state methods
Return transaction in download finished notification

Also, do not notify update when finished.
Notify download pauses and cancellations
Fail transaction on canceled and failed downloads
Support multiple downloads
update => updated
Reset state
SKDownload unit tests
Remove redundant restore transactions state