Make changes to gender-neutral and gender-specific terms

[jmccrae]

Fix #883

This introduces two new properties, masculine and feminine as synset relations that indicate a masculine or feminine form.

If the hypernym is a gender-neutral the feminine link points from the gender-neutral term

actress ==hypernym=> actor
actor ==feminine=> actress

If there is both a masculine and a feminine term both are linked from the gender-neutral term

representative ==feminine=> congresswoman
congresswoman ==hypernym=> representative
representative ==masculine=> congressman
congressman ==hypernym=> representative