MOB-29: Content Storage Lifecycle Management

- Some collapsing of common code in Constraint hierarchy.
 - Added aspect 'cm:storeSelector' with property 'cm:storeName'.
 - Defined a new, unused content store 'storeSelectorContentStore' (see content-services-context.xml).
   If this store is used, then setting the 'cm:storeName' property will force content to be stored in one
   of the named stores.  A LIST constraint is indirectly enforced for the 'cm:storeName' property.

git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@14329 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/service/cmr/dictionary/Constraint.java

@@ -56,7 +56,7 @@ public interface Constraint
     /**
      * Returns the parameters passed to the instance of the constraint.
      * 
-     * @return Map of parameters, null if there are no parameters
+     * @return Map of parameters or an empty <tt>Map</tt> if none exist
      */
     public Map<String, Object> getParameters();