Support uploading zip files

A user has a zip file containing pdf documents (For example the kind o fzip files we produce). The user wants to sign all of them in one go without having to extract them.

This can be useful in case user A signs a bunch of documents, emails them to user B, and user B wants to sign them all too.

Questions:

• What happens if there are non-pdf files in the zip?
• What happens if there are directories, and files with the same name in different directories?
• Does JSZip support this?

Todo

• Basic ZIP decompressing and queuing
• Support for folders in ZIP files
• Fix filename in external auth process
• Mime-type detection of files in ZIP for filtering mime-types