Support for undefined in selects

[stitot]

Would be great to be able to use undefined as value in selects, alternatively an option to delete the option from config.

E.g.

title: {
    text: 'Main title',
    align: 'left'
},
subtitle: {
    text: 'Another title',
}

If subtitle.align is undefined then subtitle inherits title.align. As far as I can see there is no way to set this up i Controls. Needs either the option to have 'undefined' as valid value in selects (that preferable deletes the property from config), or a separate delete action in the GUI. I can see the need for the latter in ALL input types.

[TorsteinHonsi]

Probably a nullable setting/attribute should be added to all control types, which would add a checkbox thing next to the control.