Feature/reverse proxy

As you can see below, this PR includes two changes:

* [ ] Mandatory settings for working OAuth behind a reverse proxy and
* [ ] Updated git mechanics and instructions.

We should discuss first before merging, because I believe both commits have their quirks that we have to evaluate first:

1. Why was baseUrl prepared in the code, but not used?
2. Why has it been that `this.remote` and `this.branch` have been `undefined` before this change?

Next PR: Persona :). (But not today.)

*Note:* I'm using this in production on http://wiki.transformap.co.
Yes, of course! I'm not setting the variable here, just comparing.
Sorry, I'm not native to JS yet, but it's approaching to me. Fast.

Next up, as I pointed out already, Persona and then Etherwiki based on patterns deriven from https://github.com/elf-pavlik/mdwiki/tree/etherwiki `&&` https://github.com/elf-pavlik/webserviced/tree/etherwiki, before maybe switching to https://github.com/xwiki-contrib/chainpad (found via https://github.com/cjdelisle/cryptpad)