Composition policy takes child instance

The composition policy now takes a child instance instead
of the child type, as in all cases we have access to the child
object.

This allows new-style objects to be contained by old-style objects.

Updated all composition policies to use standardized argument names
instead of `context` and `candidate`; this makes it easier to
understand.

Updated AddActionProvider to hardcode the object types supported.

platform/commonUI/edit/src/creation/AddActionProvider.js

@@ -66,9 +66,7 @@ define(
             }
 
             // Introduce one create action per type
-            return this.typeService.listTypes().filter(function (type) {
-                return self.policyService.allow("creation", type) && self.policyService.allow("composition", destination.getCapability('type'), type);
-            }).map(function (type) {
+            ['timeline', 'activity'].map(function (type) {
                 return new AddAction(
                     type,
                     destination,

platform/commonUI/edit/src/creation/CreateWizard.js

@@ -56,16 +56,16 @@ define(
          */
         CreateWizard.prototype.getFormStructure = function (includeLocation) {
             var sections = [],
-                type = this.type,
+                domainObject = this.domainObject,
                 policyService = this.policyService;
 
-            function validateLocation(locatingObject) {
-                var locatingType = locatingObject &&
-                    locatingObject.getCapability('type');
-                return locatingType && policyService.allow(
+            function validateLocation(parent) {
+                var parentType = parent &&
+                    parent.getCapability('type');
+                return parentType && policyService.allow(
                     "composition",
-                    locatingType,
-                    type
+                    parentType,
+                    domainObject
                 );
             }