Add documentation to sections

[multiscan]

Sections model should contain rich text explaining what we expect the section to contain and what the section will automatically contain. Example, the teaching section will in any case contain the list of PhD students and the list of courses for the semester. This should be written to prevent people from adding the same info in free boxes.

We should also add popup tips for most of the other fields to explain in detail the scope/role of data. Example, the now cancelled yearly achievements model had rules ensuring that achievements of past years were no longer visible.

If we hope to avoid that people fill the DB with garbage as we have now, we have to be clear about what we ask them to provide as content.