Our SingleFileZ integration would save images inside directories following the
SingleFileZ format. However, Zotero does not support syncing sub-directories of
attachments. This commit switch back to a single HTML file with base64 encoded
resources. We think that the 33% increase in resources will be offset by the
compression of HTML and removal of JavaScript and unused CSS.
This commit does not fix past snapshots that were saved using SingleFileZ.
76ae5d9f59