Add JavaScript Hooks to fileUpload

Allow to add a listener for "progress",
(and "complete", "error", "abort")

The idea is to be able to implement a progress bar without any need to write an own upload servlet.
#### Affected Versions
[2.2]

Start by locating the fileUpload client-side implementation and its existing upload lifecycle. Determine where progress, complete, error, and abort events can be exposed, then verify that listeners can support a progress bar without a custom upload servlet.

Written by the indexing model from the issue text.