Allow arbitrary nesting of modules

[JavierCladellas]

Currently the toolboxes or case-study page layout only allows to have one sub module ( or level ).
Either, the toolboxes layout filtering should be updated to create a hierarchy based on tags, or a new page-layout should be defined.
This can be useful to tackle the following pages structure problem, as an example:

• Machines
  • Machine A
    • Application 1
      • A-1.adoc
    • Application 2
      • A-2.adoc
  • Machine B
    • Application 2
      • B-2.adoc
• Applications
  • Application 1
    • Machine A
      • A-1.adoc
  • Application 2
    • Machine A
      • A-2.adoc
    • Machine B
      • B-2.adoc

It would be possible to create the previous structure without needing to duplicate, for example, pages A-1 for case A>1 and 1>A
Also, we could have more nested deeply structures if needed.