Enable automatic import of simulations for scenarios

[qacwnfq]

Right now the import_simulation command expects user input to determine whether to replace existing scenarios or to append to them. This is a hurdle for automatic upload.
By adding a command-line switch for the decision, automatic upload is made simpler.

E.g.
If the switch is not given, the behavior is the same as now
if the switch -r is given, the old simulation is replaced
if the switch -a is given, the new simulation is appended to the old one