cannot export big documents using the clipboard

Let say we have selected documents in the clipboard that include large content.
When we're trying to export them using the clipboard manager, we're getting an "out of memory" exception.

Problem is that the clipboard manager build a zip in memory. We want to put the content instead in a tempory file before returning it to the web client.

Impacted code is located in org.nuxeo.ecm.webapp.clipboard.ClipboardActionsBean.