feat(ToastContainer): add props.preventDuplicates suppory
feat(ToastContainer): add props.preventDuplicates suppory

* Thanks to @RangarajKaushikSundar 
* Original commit: 00817d9bb91a285204c71d444c640b183ab1976d
* Original commit: 87e38e45b7d5ae3ab33e39ab0d37c8c6ac50ddd6
* Closes #58 
* Closes #56 
* Closes #53 
tomchentw/react-toastr,AllenFang/react-toastr,AllenFang/react-toastr