Backbone AAI documentation consolidation

I consolidated the backbone documentation from KIT and DESY into a single section for the HIFIS Cloud Documentation. Over the course I eliminated one indentation level in the navigation and reformulated some sentences, also rephrased some bullet point lists into body text, where appropriate.

Please let me know if there is any outdated, missing or misleading information in the pages. I would like to know your opinion about the general organisation as well. Let's discuss this here.