Add generated titles for user and dev guides

Fixes #765 (closed).

This is probably not the cleanest solution, but it's i18n friendly (titles are translated for all languages) and since we don't add many guides should be good enough. Feel free to propose a better solution.

I adapted the content of the guides in english (some had a title in the body of the guide, some didn't) but i didn't edit the other languages because it's really a lot of documents in a lot of languages and would take a lot of time to edit them all. Most of those guides are untranslated anyway, and the original guides in english need to be heavily updated, so i guess better fix the translated guides then.