Migrating analysis to a laptop or another computer

[jonwright]

Our dataset object has an analysis path and a number of hardwired filenames with paths inside it.
We could make all file paths relative to the dataset object.
We could also make all the file paths relative to the analysis path.

It means making up some test case, moving it to some other folder, then seeing what breaks when it is moved.

[jonwright]

This is partly addressed by #357

It is still not at all "obvious" how to do it.

Next step seems to be:

• remove all the filenames from the dataset object
• put them somewhere else.