List/Dict: Add value property

Add the `value` property to the `List` and `Dict` classes, to make them
more consistent with other base type classes.

aiida/orm/nodes/data/dict.py

@@ -75,6 +75,14 @@ def __eq__(self, other):
             return self.get_dict() == other.get_dict()
         return self.get_dict() == other
 
+    @property
+    def value(self):
+        return self.attributes
+
+    @value.setter
+    def value(self, value):
+        self.set_dict(value)
+
     def set_dict(self, dictionary):
         """ Replace the current dictionary with another one.
 

aiida/orm/nodes/data/list.py

@@ -56,6 +56,14 @@ def __eq__(self, other):
             return self.get_list() == other.get_list()
         return self.get_list() == other
 
+    @property
+    def value(self):
+        return self.get_list()
+
+    @value.setter
+    def value(self, value):
+        self.set_list(value)  # pylint: disable=no-member
+
     def append(self, value):
         data = self.get_list()
         data.append(value)