Allows a react element for title

[michaelAndersonCampingWorld]

I'm not sure if this is going to be acceptable, but I thought I'd give it a shot. I was using this library and wanted to put styled text in a NoticeWidget. However, this library warns on that because the proptype of title is string only. Because the widget mixin supplies the proptypes for everything I think it's difficult for me to just change the proptypes of the noticewidget.

So, I'm hoping that this library can support <Text /> in the title and that we can figure out a nice way to make that happen.