Set node parameters to private.

@PascalGohl , @omaris 

Proper style with parameters is to have them in the private to the node, not the public namespace. :)
So you can edit them from the command line (_camRate:=5 will work) and they're in the correct place on the parameter server (i.e., /visensor_node/camRate, not /camRate). Currently in order to change the rate you have to set the global parameter and it's a pain.