Add node to cluster command

I've introduced new commands to mongooseimctl - **add_to_cluster** and **remove_from_cluster** that simplify clustering procedure. Moreover I've added *add_table_copy* to all mnesia modules, it is useful when configuration changes and new modules with mnesia tables are added, then it will create replicas. 

Is the *add_table_copy* going to break anything, should all the tables have replicas on each node?  
Maybe it is a good idea to make it configurable?  
I would print the $MNESIA_DIR in this message also just to make it more clear what to remove.