Hue needs a 500 template

Hue can, in certain cases, get into a situation where it will throw an exception (often for a 404) that Django tries to render through a 500 template, which we don't have.

Turning debug mode on installs a nice 500 template, but at the known cost of caching the db queries and using memory. If we turned off the latter feature, we could perhaps leave debug on and take advantage of the ready-made 500.