Split Button Implementation:
Added DynamicDropDownMenu( can add to drop down via .add method)
DropDownMenuWidget (made drawDirectionalArrow virtual)
Added Factory for DropDownMenu and Split Button
Add/used Factories in View3DWidget
Merge branch 'development' of https://github.com/MatterHackers/MatterControl into local_development
Cleaned up splitButton implimentation
Merge from Origin Development
Merge pull request #114 from mmoening/development

Updated Split Button Implementation