Exclude files while doing a filesystem backup

[ghost]

If the user wants to backup a folder from the filesystem, we should provide him the possibility to exclude certain files.
A good practice would be a list of regex paths which should be ignored.

We could also think of a .lifeboatignore file. This file wouldn't make sense in terms of backing up the files of another application, but e.g. if a user wants to backup his local PC it would be a great feature.