Add ability to retry errored file uploads

[kartik-v]

New plugin properties added:

• retryErrorUploads: boolean, will determine if errored out thumbnails can be retried for upload and submitted again.
• fileActionSettings.uploadRetryIcon: Will change the icon of the upload button to retry icon specified here.
• fileActionSettings.uploadRetryTitle: Will change the title of the upload button to retry title specified here.
• msgUploadError: will be displayed within the progress bar on the errored out thumbnails.

Other enhancements include:

• resetting progress bar correctly
• enhancing upload validation behavior so that if retryErrorUploads is false, then no upload button is shown on the file thumbnails.