Updated centerOrigin functions with the option to center on a single axis.
Reversed course, the ButtonContainer's and TabContainer's ctor no longer
take the sf::RenderWindow, sf::View, and sf::Transform arguments. Because,
sf::Transformable::GetTransform() would need to be called in the ctor and
the object is still not initialized. Also, added the setVisualScheme()
method.
Added a Increment and Decrement UI class.