Added feed aggregation module.

Redesigned the CMS_BLOCK system,
   - added condition attribute. It can be set via configuration file
     with
     [blocks]
      {blockid}.region={region_name}
      {blockid}.conditions[]=is_front
      {blockid}.conditions[]=path:location-path/foo/bar
   - For backward compatibility, the CMS will check only conditions for block name prefixed by "?".
Improved the configuration library to support list and table properties.
Updated theme for now, to include the feed examples.
Added "cache" classes, to ease caching of html output for instance. (TODO: improve by providing a cache manager).

src/hooks/cms_hook_core_manager.e

@@ -138,6 +138,9 @@ feature -- Hook: block
 
 	invoke_block (a_response: CMS_RESPONSE)
 			-- Invoke block hook for response `a_response' in order to get block from modules.
+		local
+			bl: READABLE_STRING_8
+			bl_optional: BOOLEAN
 		do
 			if attached subscribers ({CMS_HOOK_BLOCK}) as lst then
 				across
@@ -147,7 +150,16 @@ feature -- Hook: block
 						across
 							h.block_list as blst
 						loop
-							h.get_block_view (blst.item, a_response)
+							bl := blst.item
+							bl_optional := bl.count > 0 and bl[1] = '?'
+							if bl_optional then
+								bl := bl.substring (2, bl.count)
+								if a_response.is_block_included (bl, False) then
+									h.get_block_view (bl, a_response)
+								end
+							else
+								h.get_block_view (bl, a_response)
+							end
 						end
 					end
 				end