Rework parsing clean

Hi,

This is a parsing rework : 
  * All field of all object are pythonized when instanciated.
  * Default values are now correct for a given field
  * Non listed filed are "guessed" as String property by default

This also fixes some bugs : 
 * Maformed parameter in shinken.cfg are parsed better
 * register parameter in item object is now used but not inherited.

I'll merge this in a few days. Feel free to give feedback :)