Neglect aspects of the pickle state file if workflow, parameters or inputs files change their md5

[pcm32]

Currently on changes of the execution of a workflow on a directory, some changes in the workflow, parameters or other files might not be picked up in favour of the pickle state saved. Elements of the pickle state should be made obsolete if the originated element on disk shows a change. This could be either checking the MD5s of the files (and keeping that) or relying on the modification dates of the input files in general (although this could lead to issues if an older file is moved into the directory, so maybe not the best approach).

Most likely the change should happen here:

https://github.com/ebi-gene-expression-group/galaxy-workflow-executor/blob/develop/run_galaxy_workflow.py#L152

so that if the state is None or the md5 for the workflow file is different (which would need to be stored in the state before hand), then this would need to be read from disk (because the file might have changed).

[pcm32]

Alternatively, one could just warn the user that the files seemed changed and that he/she should either delete the state file or re-instate the older files.

But it still implies keeping some record of the checksum of the files to be able to detect this.