Remove overlapping content with okenos-guides

This is the initial commit of the okeanos-helpdesk branch.
The main purpose of this branch is to:
* Move non-technical parts (e.g examples) to the okeanos-guides docs,
  where they can be presented in a more user-oriented way
* Correct minor omissions that okeanos-helpdesk has encountered during
  the testing of the image-creator tool