SelectOutput should be able to disable particle types completely
SelectOutput should have the ability to delete particle types completely from the outputs.
Example behaviour:
select_output.yml
Default:
All_Gas: off
All_Star: off
All_DM: off
All_BH: on
We should be careful to ensure that when this is activated the metadata in /Cells/PartType{X}
is also removed for the relevant particle types.