Loads an attachment asynchronously and emits onUpdate event when it is done.
For the moment nothing is monitored after the image is loaded. This API was intended for versioned objects, where the versioned object is monitored for new version.
Get the attachment synchronously
if undefined, either monitorAttachment has not finished loading the data or was never called
Cleanup the instance.
After this function is called this class cannot be reused.
This cache caches attachments stored as blob descriptors.
This is necessary, because on rerender of chat messags we do not want to load attachments again. This would take too much time because we would have to load them and the browser would have to decode them again.