New switch --filter-models X which restricts the list of models used from
a directory to those that match the filter X. Currently, this can refer to
the number of states and/or the model type. Examples:
* prism-auto . --filter-models "states>100 and states<10000"
* prism-auto . --filter-models "model_type=='DTMC'"
* prism-auto . --filter-models "'MC' in model_type"
The model metadata is by default read in from a models.csv file (as found,
for example, in the PRISM benchmark suite). The name of the file used can
be changed with --models-info FILE.