Improve build (and dox) to allow easy dev work

[Trevor-van-L]

Currently when testing locally you have to manually switch all the URLs to point to localhost instead of Tsitu. This is a pain in the pita. We should instead have a build flag decide which URL to point at. This decreases the likelihood of someone committing localhost URLs too.

Xellis suggests looking at webpack.

Xellis also suggests customizing http-server to disable caching and allow CORS from all origins in the dev build

This should all be documented