Feature/reverse proxy

To be done:

* [ ] exclusion of git mechanics commits and reinvestigation of the issue
* [ ] comparison of `baseUrl` is to correct to `==`

---

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.
I found the bug (which is pretty bad, actually), and I am going to fix it right now.

I will also integrate the other changes you made in this PR. After that I will close it.

I will keep you posted.