adding ability to set selected toggle for dropdowns

Using ofxUI is fantastic (so first off, thx!) but I was kinda surprised to find that (unless I'm missing smthg) there wasn't a way to programmatically select an specific toggle from a dropdown.  This is useful for when you have to dropdowns, and the value of the second one should change based on what the user select for the first one.

Or, if you loading saved settings from XML and want to populate the value of the dropdown.

This doesn't yet take into account dropdowns with multiple selections.