Allow working with tibbles

[shaunss]

Feature Request

Currently goldfish assumes that network data is a data frame. But some more R packages (especially from the tidyR family) prefer tibbles for tabular data. goldfish works with tibbles, too, but it throws a warning:

data("Social_Evolution")
calls2 <- as_tibble(calls)
callNetwork <- defineNetwork(nodes = actors, directed = TRUE)
callNetwork <- linkEvents(x = callNetwork, changeEvent = calls2,
                          nodes = actors)

> Warning:
> Unknown or uninitialised column: `replace`.