NSOperationSubclass added
Migrating code from PhotoManager into DownloadImageOperation
PhotoManager now an instance in list and detail VC
Setting operation dictionary in init, and adding logic to store based on index path
Checks in place added to make sure operations aren't retained by operation dictionary and are removed correctly on completion
Taking into account if the operation is cancelled
Added method to cancel an operation given an index path
Added cancel method to header file and a bit of documentation
Braces missing from cancel check
Cancelling operations added
Changed to using nsurlconnection instead of querying with nsdata
Removed debugging code
Merge branch 'feature/image_operation' into develop