Consistently Apply Nightwalker Style to Download/Upload Pages

[joshft91]

@CallMeBruce, here are a couple more small cosmetic changes.

For some reason, the nightwalker.css style was not being applied to the download and upload pages. I believe it has to do with the way the pages render in the client.js or mocha-init.js scripts, though I don't know enough about how those work to know why.

By adding nightwalker.css to the pages after the style.css is applied, the download/upload pages now follow the same look as the preferences.html page (which inherits both styles from the index.html, I believe)

download.html before/after

upload.html before/after