Add UploadPhotoTask for queued uploading

UploadEligibilityChecker now checks multiple photos in one request, for better efficiency.
UploadPhotoTask allows queuing of uploads into a separate ThreadPool, so that it now is possible to have loads of threads scanning the local file system, but only one thread checking for upload eligibility, however in a bulk fashion. 
This effectively allows for numerous threads to scan to local file system without over using the web service.
Various fixes