Support a list of trajectories as input to branch or clone

[Enchufa2]

As join does.

[Enchufa2]

If #143 is considered, we could write:

large_number_of_trajectories <- lapply(1:N, function(i) {
  trajectory() %>%
    ...
    seize(paste0("resource", i)) %>%
    ...
})

trajectory() %>%
  branch(some_function, continue=TRUE, large_number_of_trajectories)