Bootstrap CSS sets the max-width for images to 100%. This makes it so
OpenLayers maps don't render (the layer container has 0 width, so all images
are given the same). Even if our layer container had a more sensible width
(e.g. 100% of the viewport), we would still have issues with tiles that are
larger than the viewport.
Since the OpenLayers stylesheet may be loaded before or after bootstrap.css,
we should use !important when setting the max-width to none for images we
control.
