Split the nginx upload page #463

@renato2099

From the review of PR 437 (comment):

one thing to note is that we will have to split this file shortly, it is already quite large+complex (it's not going to be maintainable by humans at this rate)

services/nginx/proxy/upload.html is one file of markup, styles, and the job-polling script. Split it before the next upload change so a person can maintain it.