move part of --chain inside the container

[johanneskiesel]

• mount the chain output directory, not just the run-specific output directory
• write and update a file in the chain output directory that specifies the last output directory and how the following output directories should be called (perhaps using a setting that specifies the name of that file). the update should happen after the run was successful
• use that file to determine the input and output directory if it already exists

The idea is that scriptor can then be run several times with the same command line, automatically continuing where it left. This will allow easier use in Kubernetes

[johanneskiesel]

done as part of 0.9.0