Reorganize folder structure for .md files

[omikron-fp]

Current behaviour

• Project's folder structure is different from the app's UI structure. This may be confusing at times.

Expected Behaviour

• Project's folder structure reflects the app/s UI structure

Notes

Main source of confusion is the api folder.
In the UI there is an API and a Documentation section. Relevant files for the API section are located in the markdon/en/{root} AND markdown/en/api.
While all files relevant to the Documentation section are located in markdown/en/documentation.

In the codebase the term guides is used to describe documentation.

Suggested folder structure

markdown
  de  // possibly redundant
  en
    api  // non-.api files from the 'root' directory move here
      ff-searchbox.md
      ff-searchbox.api.md
      [...]
    documentation  // unchanged
      instal-dist.md
      [...]

Beware!

All changes in progress might have to be merged before this issue can be solved to avoid nasty merge conflicts.

@omikron-fp is this still relevant?

[omikron-fp]

Folder structure hasn't changed yet. So yes, it's still relevant.