feat(OverlayView): allow rendered as children of MarkerCluster
feat(OverlayView): allow rendered as children of MarkerCluster

* Let `OverlayView` be clusterd in `MarkerClusterer`
* Thanks to @ziad-saab 
* Closes #187 
jossi87/react-google-maps,RishabhJain96/react-google-maps,joshcarr/react-google-maps,RishabhJain96/react-google-maps,jossi87/react-google-maps,tomchentw/react-google-maps