#
Define default behavior for items in the list.
    PropDefinition
  
  By defining a wildcard property ("#") on the prototype, this will supply a
default behavior for items in the list.  The default wildcard ("#") definition
makes every item run through the "observable" types converter.
It looks like:
"#": {
  type: "observable"
}
Setting the wildcard is useful when items should be converted to a particular type.
var Person = DefineMap.extend({ ... });
var People = DefineList.extend({
  "#": Person
});
The wildcard property has optional added and removed functions that will be called after
an item is added or removed from the list with this being the list.
var People = DefineList.extend({
  "#": {
    added: function(itemsAdded, index) { ... },
    removed: function(itemsRemoved, index) { ... }
  }
});