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/admin/handler/cms_admin_export_handler.e

@@ -69,8 +69,7 @@ feature -- Execution
 					else
 						create l_exportation_parameters.make (api.site_location.extended ("export").extended ((create {DATE_TIME}.make_now_utc).formatted_out ("yyyy-[0]mm-[0]dd---hh24-[0]mi-[0]ss")))
 					end
-
-					l_response.hooks.invoke_export_to (Void, l_exportation_parameters, l_response)
+					api.hooks.invoke_export_to (Void, l_exportation_parameters, l_response)
 					l_response.add_notice_message ("All data exported (if allowed)!")
 					create s.make_empty
 					across