Drop access to props.value to avoid bugs

[malte-wessel]

Explain the problem

Right now it is possible the access the props' current value by calling props.value.
This might lead to bugs where a property is updated, but we still have an old reference to it.
We should find a way to deny access to this property.

// Dangerous!
const List = ({ props }) => {
    const { items } = props.value;
    return combine({
        items
    });
};

// Correct way
const List = ({ props }) => {
    const items = props.pipe(pluck('items'));
    return combine({
        items
    });
};