default ColumnLabel label() {
        return ColumnLabel.of(this);
    }
Returns a label that can be used as key in a map. Using the ColumnIdentifier itself
does not work since there are generated enums as well as runtime created ColumnIdentifierImpls
that are considered to be equal but have different hashCode.

All implementations of this interface will, however, have equal
{@code label()} iff they refer to the same column.

@return a ColumnLabel that is unique for this particular ColumnIdentifier
runtime-parent/runtime-config/src/main/java/com/speedment/runtime/config/identifier/ColumnIdentifier.java