Add dump algorithme.
To add a server to the existing structure :
- edit the file servers.xml => contains the list of the existing server
	- Add the new one
- Launch : java -jar Server.jar <serverIDInXmlFile> 1
- The server will make the things to join the system

The backup algorithme work also.
Test to do :
- dump with queries coming from client.
Remain : 
- failure detection
- Change leader