addGeometry(definitionID, vertices, uvs) {
        this.geometries.push({
            id: definitionID,
            vertices: vertices,
            uvs: uvs
        });
    }
Add a geometry to our cache if not already in it

     params:
     @definitionID  (integer): the geometry ID to add to our cache
     @vertices (array): vertices coordinates array to add to our cache
     @uvs (array): uvs coordinates array to add to our cache
*