Add a lot of error handling in document.tasks + some refactoring + code style
Use "pdfinfo" instead of "gm identify" to compute a pdf lenght and boost perfs o/
Stop using gm for the thumbnails size computation and use a much faster python alternative
add the ability to filter the .children() method to exclude models or allow only some models
use this new functionality to hide Page objects from the generated graph (./manage.py todot)

+ code style
Merge branch 'master' of github.com:C4ptainCrunch/beta402 into documents