Add synonym type superproperty for most_common_name

[cthoyt]

Closes #207

This PR makes sure that the most_common_name is exported as a synonym type definition in OBO by adding a a parent annotation to http://www.geneontology.org/formats/oboInOwl#SynonymTypeProperty

The OBO export from the edit file now looks like this, so I'm assuming that duing build that this will get propagated properly

format-version: 1.2
subsetdef: local_breed "refers to a breed reported in single country, as defined in DAD-IS (https://www.fao.org/dad-is)"
subsetdef: national_breed_population "refers to the instance of the transboundary breed in a particular country, as defined in DAD-IS (https://www.fao.org/dad-is)"
subsetdef: transboundary "refers to a breed reported in several different countries, as defined in DAD-IS (https://www.fao.org/dad-is)"
synonymtypedef: most_common_name "most common name"
idspace: dce http://purl.org/dc/elements/1.1/ 
idspace: dcterms http://purl.org/dc/terms/ 
...