Collection upload fixes

This PR introduces various collection upload fixes:
* change "Upload" button type from "submit" to "button" (this bug caused the whole form to be submitted)
* change icons to FontAwesome
* replace non-working progress bar with a spinning cog icon indicating that upload is in progress
* render editable fields for uploaded files (async) and capture the submitted data in the eventlistener to bind it to the object being created
* add sanity check in ReorderCollectionListener to prevent PHP warning messages
* add displayDownloadButton option, to further customize the widget behaviour
* remove the "disabled" class to make the "delete" checkbox clickable again