Coloring and grouping page

[RafałOrchowski]

During development for large processes, time is wasted on finding the right page. 
This can be sped up by organizing the pages, but it would be faster and easier to read if the pages could be grouped and/or colored.
Groups could be rolled up and expanded as needed.

[PvD_SE]

We currently do grouping by page number, eg 1, 1.1, 1.2, 2, 3, 3.1 etc. This is tedious to maintain if changes to the structure are made later on. A color scheme sounds like it could be maintained more easy.