Improve the web services overview steps and checks

I've been working with a bunch of 3rd party developers later, these are people who routinely work with lots of apis but are new to moodle. They consistently seem to have trouble getting started and running into silly issues getting WS working and I think the UX of the overview could be improved a lot to guide people through it.

Roughly what I think could be improved:

1) every step is ordered so its dependencies are earlier

2) this means we can have hard checks at every step, ie a count of users who have capability X

3) every step should have 2 links, a link to do this step, and a link to confirm what has been done in this step

4) the api docs should be deep linked from here

5) the api docs should be able to be public and not need a token

6) the api docs should be able to be produced in the context of a token and have a complete example for each function in -situ. Ie you can choose a language and it will give you exact code you can cut and paste and just run. The MVP would be bash 1 liners for curl, but the next language would be php. Each language could be some sort of set of mustache templates or might need to be its own sub plugin type. See also MDL-45557