Add project name, when running dead_code_detector in multiple legacy projects

[tilo]

when an org has multiple legacy projects, using a shared redis,
it can be useful to build the name of the specific project into the redis key, e.g.:

        "dead_code_detector/record_keeper/#{project_name}/#{class_name}/class_methods"
        "dead_code_detector/record_keeper/#{project_name}/#{class_name}/instance_methods"

[dpep]

a custom prefix could be useful