Reorganize the Examples section of the webpage

Problem:

• no sane order of examples (page starts with feflowlib which is a bit too specific and complex for not advanced users)
• examples are split into sections by the subpackages they belong to not by their place in the workflow
• lack of consistency in structure within examples (some authors don't use headings at all, some do, others number sections but not make them into headings)

Solution:

• this MR introduces sections based on the typical workflow steps
• added a Quick Start section at the beginning of the page covering the most basic features of ogstools

Other:

• section authors are removed, example authors are left untouched

TODO:

• introduce some consistency to the structure of the examples