Split and merge function for diffnet objects

[aoliveram]

We need to have a function that allows us doing the following:

obj <- rdiffnet(... multiple behavior ...)

# If we wanted to split it
objs <- split_behaviors(obj) # So then objs is a list of diffnet objects

# We could also go back
obj1 <- combine_behaviors(objs)

# And we should have
obj == obj1 # TRUE

Because this way, instead of having functions doing:

if (multi.behavior) {

} else {

}

We could have them

# Start off by splitting (if it is a single behavior, will return a list
# with a single object
diffnet_list <- split_behaviors(diffnet_object)

# So both single and multiple have the same implementation
for (diffnet in diffnet_list) {
  ...
}