includeSelectAllDivider option

Add an optional `includeSelectAllDivider` option to add a "divider" immediately after the "select all" option

![screen shot 2014-03-04 at 12 00 20 pm](https://f.cloud.github.com/assets/97612/2325725/6950fea8-a3d9-11e3-8c83-3f9626ade75f.png)