Fixes DS-2113: JSPUI HTML5 upload should store Bitstreams...

JIRA: https://jira.duraspace.org/browse/DS-2113
Currently the HTML5 upload in JSPUI submission stores uploaded files in the session and creates the necessary Bitstreams not until the user clicks the next button. So there is a time where the UI alredy shows a green check mark but the file is not stored safely in the repository (after upload, before the next button is clicked). A PR to change this is in preparation.

- [x] JSPUI person to test/verify