Download implemented (send file to client interested on it)

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Critical:
//TODO: supernode remove client's files from hashtable
//TODO: supernode tell other supernodes to remove files

Needed:
//TODO: add better messages in classes in packages server and supernode

Bonus:
//TODO: send all files to new supernode associated (when reconnect), instead of set hashtable as new
	  Can be done on method connetc in Client.java