Customize toolbar items (both toolbars: topToolbar, toolbar)

I have the same issue with MWPhotoBrowser. There is no way to add new button or something like that. I have added additional method to add toolbarItems and moved "Done" button into toolbar. In such controls it's better to give developer more flexibility. Also, I've updated example with "Customized Photo Browser" section. You can see two additional buttons on topToolbar and on bottomToolbar. Also suggestion to rename toolbar -> bottomToolbar.
Thanks!