Mobile diff viewer, allows for a top-down rendering of diff fragments which is

friendlier for mobile devices. Contains a bunch of CSS stylings only to be

applied when screensize <= 720px, most of which aim to eliminate wasted space.
Top-down view is achieved by allowing client to request an alternate rendering

of the diff view using query parameter ?view=top-down, which then sets the

context variable is_mobile to true in the diffviwer/diff_file_fragment.html

template, which applies/shows mobile styles/elements.

Beautifulsoup was included as a dev-requirement for adding some CSS-selector-

like functionality within Python tests, so that specific elements of the

templates returned by Django could be tested while still having the tests

purpose be explicit and comprehensible.
Includes javascript test to assert correct AJAX request is made for top-down 

diff view on when screenwidth <= 720px. 

Also has some Python tests asserting correct view is returned for diff fragments 

with view=top-down query, as well as correct classes and stylings are applied.