basic support for importing arbitrary series

this works now:

m <- seas(AirPassengers,
     transform.function = "log",
     regression.variables = "td",
     arima.model = "(0 1 1)(0 1 1)12",
     forecast.save = "forecasts"
     )

m$series$fct
mod_spclist does not overwrite arguments anymore, just adds new ones
also imports non time series
universal data import