[GMG-Devel] PDF support

[Sebastian Spaeth]

Hi all,
here is my first and rough cut at a PDF supporting media handler.

This is commit 566fdd79e3bf44cf92e2cada4bf987fee10b4fde in my branch 
media_handler_pdf at git://gitorious.org/mediagoblin/mediagoblin.git.

Patch was too big to be attached, see here: 
https://gitorious.org/~spaetz/mediagoblin/spaetz-mediagoblin/commit/566fdd79e3bf44cf92e2cada4bf987fee10b4fde

Some comments on the state of things:

Uploading of PDF works. So far, downloading does not work, as I simply 
use the "image preview" template and that attempts to stick the pdf in a 
<img> tag, but that's only a matter of creating a PDF specific template.

What remains to be done:
  - the gallery object template somewhere prefixes "/mgoblin_media" to
    the thumbnail URL, even if we want the default thumbnail starting
    with a "/mgoblin_static" URL. THis prevents the default thumbnail
    from being displayed at the moment.
  - Create a HTML template that suits PDF file better
  - Actually extract some metadata from the file (author, description,
    created on, created with, ....)
  - Display the real first page as a thumbnail, needs converter
  - The thumbnail icon is hardcoded for now. This needs to get the value
    from ./__init__.py:MEDIA_MANGER['default_thumb'] but I don't know
    how to access that value from processing.py.

Longterm: Use pdf.js to actually display the PDF file?!

I am giving up for now, but I think merging in this code post-release 
would be a good foundation to get something better going. My biggest 
roadblock is the auto-prefixing of "/mgoblin_media" somewhere and I need 
to track that down.

Sebastian