endpoint and form to upload non-XML files

[dariok]

Currently, the upload form and endpoints only really deal with XML files.
While these are most important (to ensure retrieval by ID works), uploading other files as well is useful (no need to use other tools to upload these files)

• create an endpoint to deal with BLOBs
• update form and JS to accept BLOBs and use their relative path (and some hard coded mappings) to put them into the correct collection