clear up the folder structure

[akleinau]

This is intended to ease the way for newcomers to the ontology by having a clear and understandable folder structure.

• move example sheets in the example folder
• add new example sheets/ sheet versions
• delete outdated ontology files: oeo_geo.omn, scenarios.owl

This just clears up the github folder/ file structure to make clearer which files are important.
I saved the deleted ontology files locally to make this request easier. They weren't used or needed for over half a year and are outdated and by that just confusing for newcomers.