Implemented CMS storage for user and nodes.

Implemented role and permission storage.
Introduced the CMS_PARTIAL_NODE and CMS_PARTIAL_USER.
Added support for node storage extension
  - storage of data specific to each node content type,
  - in addition to the core CMS_NODE)
  - For now, only implemented for SQL storage.
Note: in current version, CMS_PAGE support is hard coded in the core,
    (as opposed to be only supported by the node module.)
Commented/removed for now, the Web API code to update node summary, title, via REST request.

src/persistence/cms_storage.e

@@ -22,6 +22,11 @@ feature {NONE} -- Initialization
 		do
 		end
 
+feature -- Access
+
+	api: detachable CMS_API assign set_api
+			-- Associated CMS API.
+
 feature -- Status report
 
 	is_available: BOOLEAN
@@ -39,6 +44,14 @@ feature -- Error Handling
 	error_handler: ERROR_HANDLER
 			-- Error handler.
 
+feature -- Element change
+
+	set_api (a_api: like api)
+			-- Set `api' to `a_api'.
+		do
+			api := a_api
+		end
+
 feature -- Misc
 
 --	set_custom_value (a_name: READABLE_STRING_8; a_value: attached like custom_value; a_type: READABLE_STRING_8)