Draft:Pagedjs

This is very busted, though it includes most of the pieces that are needed – I'm still cleaning this up. What this should do is basically this:

1. DownloadDropdown.js should tell page to send query to server when PDF is chosen.
2. ProductionPage should send query to server. It needs to send the HTML from the manuscript and the metadata for the manuscript.
3. The server component is server/pdfexport
4. Server should assemble data and send to pagedjs volume
5. First it checks for credentials for pagedjs, get credentials if we don't have them
6. server gets a response back from pagedjs
7. server should send back answer to page
8. page should provide option to download PDF

The first commit in this branch is a working client-side version of this which is using an external server. But I feel like my server-side code is a mess – I think that needs a lot of cleaning. Posting this with a lot of embarrassment, though I sense this isn't that far off from a working state.