fixed (w/h)Align center for containers with min width

[jonah-iden]

Fixes #106

This fixes center alignment for when the parent node or the compartments parent has a set minWidth.

How to test:
Take the class diagram example
configure the first node as follows (model-source.ts:155)

            layout: 'vbox',
            layoutOptions: {
                minWidth: 200,
            },
            children: [
                <SCompartment>{
                    id: 'node0_header',
                    type: 'comp:header',
                    layout: 'vbox',
                    layoutOptions: {
                        hAlign: 'center',
                    },
                    children: [
                        <SLabel>{
                            id: 'node0_classname',
                            type: 'label:heading',
                            text: 'Foo'
                        },
                        <SLabel>{
                            id: 'node0_classname_2',
                            type: 'label:heading',
                            text: 's'
                        },
                    ]

you shouold now see both text items are aligned correctly in the center. Previous to this fix they would be aligned left even though hAlign center was set

[spoenemann]

Thanks!