Remote reload/restart commands

This bunch of commmits is to add a new /reload web service.

Shinken has two default commands that may be interesting to be used remotely (let's say from Glpi ...) : 
 - restart-shinken, to 'service shinken restart'
 - reload-shinken to 'service shinken reload'

 I added a new /reload WS that may launch an external command RELOAD_CONFIG. This external command does not currently exists but I will propose a commit to add this command in the external commands.