Fix the depth of the ontology page list

[jmillanacosta]

The ontology page hierarchy now has a max depth of 1.

It has to be fixed into a Protege-like indentation for class hierarchy.

[egonw]

Yeah, I think of doing it like in this issue: #19

[jmillanacosta]

d3 https://github.com/ammar257ammar/PRA3006-D3-Examples/blob/main/TreeChart/index.html