Clean up multiples in the plant phenological trait hierarchy

[elhartley]

Clean up multiples in the plant phenological trait hierarchy

Related to #116 and #132.

[ramonawalls]

This poly-hierarchy is created due to the EQ axions. It is correct, but makes it very difficult to navigate the ontology. I think we could fix it by using sparql queries to slim down the ontology. I am also investigating simplifying the axioms we use to define present and absent classes per issue #62. That might not solve this issue, but we should finalize that issue before working on this one.