Add configuration file to project to support ignore and excludes

[pombredanne]

When I create a project I would like to upload also a configuration file that would then be used to configure certain aspect of the pipeline.

• The simplest need is to skip certain files based on their paths or path patterns.
• A more advanced need would be to correct and override certain scan results and findings.

See also aboutcode-org/scancode-toolkit#520
Note that there is a similar thing in ORT and it would be useful to adopt a format that either the same, or close enough to be compatible.