Document analytics (WIP)

The Javascript still needs some cleaning up, but here is a working basic first phase of the analytics page.

Features:
- column graph with number of threads, annotations, and replies requested per page (takes a few seconds to load)
- thumbnail page preview with number of threads, annotations, replies requested below
- filter and sort pages by metrics
- number of threads, annotations, replies requested below each page colored by gradient (currently in arbitrary intervals)
- hover over page numbers for enlarged view, click to view page in NB

Linked to in the files view table (under the "Stats" column) for admin only
path: /f/[source_id]/analyze