Specify where the BEAST2 output files are stored

[richelbilderbeek]

Depends on:

• Merge model_select_params and inference_params into a list of experiments #69

It should be possible to specify to pirouette where the BEAST2 output files are stored. This is essantial for both raket and razzo.

Currently, due to the model selection, this feature is lost.

And additionally, I never liked those model selection functions.

I think it's best to ditch the model_select_params in favour of a list of inference models. Each inference model must have:

• a type: generative or candidate
• a site model, clock model, tree prior
• an optional MRCA prior
• the BEAST2 input and output filenames

[richelbilderbeek]

Depends on #69

[richelbilderbeek]

Done! It is part of create_experiment()$beast2_options