Allow to conciously break consistency

[maowerner]

The emphasis of paramvalf is to always ensure consistency of the data. This is already circumvented by the -k flag. In case of an error the remainder of a dependency graph is not executed. In practice this leads to deprecated and due to the error currently not reproducible files lying around. In addition it often happens that a minor change (e.g. not using a certain parameter set anymore) makes the framework redo time-intensive parts of the analysis. One workaround is to touch the corresponding output file to fool make but I think there should be some built-in way for the user to take over responsibility.

One way would be a flag like -use gevp.Rdata which tells it to ignore changes to the dependency graph that happened before that.

One more thing is a flag --ensure-consitency which deletes all output and reproduces everything from scratch to completely rule out inconsistent data e.g. from deprecated files that are still used somewhere or not reproduced files due to -k