#104 Add single-click get-leaf-compounds feature

[Janna Hastings]

When browing the chemical entity ontology, it is very useful to be able to see a representative set of the matching leaf-level structures. This can be achieved by going to the advanced search, putting in the class id in the ontology filter with relationship is-a, and selecting the 'chemical structures only' option. It would be VERY useful to have an option to do this directly from the page of the ontology class? (The option could be named something like 'show all compounds with structures'?)