Add basic tests for document page
Uses the document id in the document page url
Allows non-unique document slugs

* This breaks the document download as it is right now
Continues using the document slug to find the correct document

Since the slug is still in the url, there's no point in not using it, and we
risk ending up like some websites that accept anything in the url and return a
valid page.
Uses the document id in the document download url
Uses document id in the URLs for visualizations
Adds basic pagination to the corpus document list

The javascript pagination does not work well for corpora that have a large
number of documents.

Next steps will be:

- allow the user to define the number of results per page
- allow sorting by filename, size, upload date and owner

We also need to implement pagination in the document list page (that is even
worse, since it shows all the documents a user has access to). In that case,
though, we can probably use [django's built-in object list
view](https://docs.djangoproject.com/en/1.3/ref/generic-views/#django-views-generic-list-detail-object-list)
Allows user to select how many documents will be displayed in a page
Allows sorting corpus documents by filename and by updload date
Uses django.views.generic.list.ListView for the document list
Adds pagination to the document list
Adds sorting to the document list
Returns 404 for pages that don't exist

This makes more sense than trying to figure out what the user wanted.
Renames a test (typo) - s/corpus/document/
Adds pagination benchmark
Merge branch 'feature/paginate-document-list-in-corpus-page' into develop

Fix #40
Fix #77
Fix #81