FlowPane minSize is too big

See the screenshot. Min width of FlowPane is bigger than its content which causes this bad layout. According to our conversation with Amy, minWidth for FlowPane should be reduced to the widest node width.

> • Pref width for FlowPane should be based on its content pref size.
No. prefWidth of FlowPane is directly related to it's prefWrapLength property. The idea is that it's preferred
size is fixed and it wraps its content.

The minWidth of FlowPane should probably be related to the widest node, so we do have a bug because I think
right now FlowPane returns it's pref width for it's min.