Added notion of "front" page.

Changed CMS_HOOK_BLOCK.get_block_view to accept only attached string for `a_block_id'.
Keep simple name in CMS_MENU_SYSTEM.
Module that implements a CMS_HOOK need now to redefine CMS_MODULE.register_hooks .
Added simple code for NODE_MODULE, in order to see something.
Added CMS_URL_UTILITIES that should be used to compute url for cms path such as "/foo/bar".
Implemented get_active in CMS_RESPONSE to update the "is_active" on each link.
Added NOT_IMPLEMENTED_ERROR_CMS_RESPONSE.
Implemented a few hooks in DEMO module, for testing.
Updated smarty template related code.

examples/roc_api/site/www/themes/bootstrap/tpl/page_header.tpl

@@ -4,8 +4,7 @@
       <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">
         <span class="sr-only">Toggle navigation</span>
       </button>
-      <a class="navbar-brand" href="${site_url/}" itemprop="home" rel="home">{$site_name/}</a>
-      <a class="navbar-brand" href="https://www2.eiffel.com/beta" itemprop="home" rel="home">Eiffel CMS</a>
+      <a class="navbar-brand" href="{$site_url/}" itemprop="home" rel="home">{unless isset="$site_name"}Eiffel CMS{/unless}{if isset="$site_name"}{$site_name/}{/if}</a>
 
     </div>