Check for no chains of "placeholder" concepts in EDAM branch

[joncison]

Placeholders ("organisational classes") are currently annotated with <usageGuideline>Not recommended for annotation in bio.tools.</usageGuideline> (we need something better) and there shouldn't usually be chains of these in the EDAM Data subontology.

This can be clarified once the Editors Guide (http://edamontologydocs.readthedocs.io/en/latest/editors_guide.html) is more settled.

[joncison]

Rule are well defined here and here,