Refactored and update CMS hooks design. (Move from CMS_RESPONSE to CMS_API).

Moved content_types and content_type_webform_managers from CMS_RESPONSE to CMS_API.
Updated the way to output content (node, ...) to html page.
   See CMS_CONTENT_TYPE_WEBFORM_MANAGER.append_cointent_as_html_to (...).
   Added notion of "teaser" (short version of the content), as opposed to full content.
One can use CMS_API.html_encoder ... when possible, same for `formats', ...
Added bridge from CMS_MODULE_API to CMS_API's encoders.
Added new CMS_TAXONOMY_HOOK used to retrieve list of content associated with a specific term.
Moved up to CMS_RESPONSE a few features which was available only in specific descendants.

Added /taxonomy/term/{termid} implementation.

modules/taxonomy/cms_taxonomy_hook.e

@@ -0,0 +1,19 @@
+note
+	description: "Hook provided by module {CMS_TAXONOMY_MODULE}."
+	date: "$Date$"
+	revision: "$Revision$"
+
+deferred class
+	CMS_TAXONOMY_HOOK
+
+inherit
+	CMS_HOOK
+
+feature -- Hook
+
+	populate_content_associated_with_term (t: CMS_TERM; a_contents: CMS_TAXONOMY_ENTITY_CONTAINER)
+			-- Populate `a_contents' with taxonomy entity associated with term `t'.
+		deferred
+		end
+
+end