Create gender API and adjust serialization of gender property

src/Bundle/ChillPersonBundle/Resources/public/vuejs/_api/OnTheFly.js

@@ -24,6 +24,12 @@ const getCivilities = () =>
       throw Error('Error with request resource response');
    });
 
+const getGenders = () =>
+    fetch('/api/1.0/main/gender.json').then(response => {
+        if (response.ok) { return response.json(); }
+        throw Error('Error with request resource response');
+    });
+
 const getCentersForPersonCreation = () => makeFetch('GET', '/api/1.0/person/creation/authorized-centers', null);
 
 /*
@@ -67,6 +73,7 @@ export {
    getPerson,
    getPersonAltNames,
    getCivilities,
+   getGenders,
    postPerson,
    patchPerson
 };