Fix broken min/max calculations on groupRef child elements

[veewee]

For reference:

• Nullable group isn't reflected in generated types. phpro/soap-client#586
• Enhance property meta with container meta php-soap/wsdl-reader#49

This improves min/max occurence calculations on groupRef elements:

   <complexType name="nullableGroupRef">
        <sequence>
            <group minOccurs="0" ref="tns:mygroup"/>
        </sequence>
    </complexType>
    <complexType name="listGroupRef">
        <sequence>
            <group minOccurs="0" maxOccurs="unbounded" ref="tns:mygroup"/>
        </sequence>
    </complexType>
    <complexType name="scopedGroupRef">
        <sequence>
            <group minOccurs="2" maxOccurs="6" ref="tns:mygroup"/>
        </sequence>
    </complexType>
    <complexType name="singleGroupRef">
        <sequence>
            <group minOccurs="1" maxOccurs="1" ref="tns:mygroup"/>
        </sequence>
    </complexType>
    <group name="mygroup">
        <sequence>
            <element name="nullable" type="string" minOccurs="0" />
            <element name="list" type="string" minOccurs="0" maxOccurs="unbounded" />
            <element name="scoped" type="string" minOccurs="3" maxOccurs="5" />
            <element name="single" type="string" minOccurs="1" maxOccurs="1"/>
        </sequence>
    </group>

Resulting in following min/maxes on the child elements:

Types:
  > http://test-uri/:nullableGroupRef {
    ?string $nullable
    array<int<0, max>, string> $list
    array<int<0, 5>, string> $scoped
    ?string $single
  }
  > http://test-uri/:listGroupRef {
    array<int<0, max>, string> $nullable
    array<int<0, max>, string> $list
    array<int<0, max>, string> $scoped
    array<int<0, max>, string> $single
  }
  > http://test-uri/:scopedGroupRef {
    array<int<0, 6>, string> $nullable
    array<int<0, max>, string> $list
    array<int<6, 30>, string> $scoped
    array<int<2, 6>, string> $single
  }
  > http://test-uri/:singleGroupRef {
    ?string $nullable
    array<int<0, max>, string> $list
    array<int<3, 5>, string> $scoped
    string $single
  }

[goetas]

Nice! Thank you for the contribution!