Implement array fields as mixins

[warownia1]

We can utilize Python's multiple inheritance and mixin classes to "convert" any field class to it's array counterpart instead of having multiple flag. The mixin would override validate() and to_cmd_parameter to work with arrays and call superclass' methods on individual values i.e.

def validate(self, value):
    return list(map(super().validate, value))

This should improve code readability and testability.