Update `model` with [[Field]] `state`
@param value [[Field]]s state
@param state [[Form]] `model`
function updateFieldsState(value, state, fields) {
    const newModel = Object.assign({}, state);
    fields.forEach(selector => {
        const prevState = selector.getValue(newModel, {});
        selector.setValueImmutable(newModel, Object.assign({}, prevState, value));
    });
    return newModel;
}