Add save feature to CObjets

inside CObject:

• store() which update the config object with the cobject cached info
• save() which does the save

On Configuration:

• i update the save() method, and i remove the dispatch.send(save.config), i am not realy sure how the previous code was working.
• i add append_string(), to easily add a block of xml at the end of the config node, but maybe it should be refactored

There is unittest with this poor GuineaPig