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.

src/kernel/form/cms_form.e

@@ -19,7 +19,7 @@ feature -- Basic operation
 
 	prepare (a_response: CMS_RESPONSE)
 		do
-			a_response.hooks.invoke_form_alter (Current, Void, a_response)
+			a_response.api.hooks.invoke_form_alter (Current, Void, a_response)
 		end
 
 	process (a_response: CMS_RESPONSE)
@@ -29,7 +29,7 @@ feature -- Basic operation
 
 	on_prepared (a_response: CMS_RESPONSE; fd: WSF_FORM_DATA)
 		do
-			a_response.hooks.invoke_form_alter (Current, fd, a_response)
+			a_response.api.hooks.invoke_form_alter (Current, fd, a_response)
 		end
 
 	on_processed (a_response: CMS_RESPONSE; fd: WSF_FORM_DATA)