* Incremental work on persistent file cache
* Rename providers to handlers
* Implement zip file caching for resumable downloads
* Implement partial download for zipped files
* Allow executing workflows using GET verb
* Implement custom header for correlating downloads
* Rename FileName to Filename for consistency
* Update interface XML comment
* Cleanup
* Fix that source Downloadables were executed even when cached zip exists
* Make download correlation ID optional