rename action methods, remove code with aws credentials
delete upload from server only if status is different than completed or uploaded.
renamed UploadViewModel.Start() to UploadViewModel.StartUpload().
renamed buttons to match view model actions' names
split message_handlers region to message_handlers and events (should be like that since the beginning!), set UploadVMToRemove = null when removing an UploadViewModel from the FilteredUploads list.
fix FileName textblock binding after renaming Pause button to PauseUpload.
just tiding up.