Enable user to exclude resources not relevant for compliance

[benedikt-richter]

As a user I want to be able to exclude files and folders that are not relevant for compliance (e.g. because they are not shipping). Examples include tests and build tooling that is not distributed.

The following seems required:

• There should be a way to mark such resources.
• Once a resource is marked there should be visual feedback. The respective folders could be displayed in grey/slightly transparent.
• These should also not be taken into account for the progress bar and other aggregated statistics.
• This choice should also be persisted and be reapplied when a file is opened again.
• All signals attached to these files should be hidden in parent.