Support specifying project ids for migration

This commit will support the specification of projects to migrate by one or more given project id identifiers, and also by a csv file list.

So long as the project.repository_storage is the same as the specified source --current-file-server=source-fqdn then only projects given by the command line argument --project=PROJECT_ID,... will be replicated to the given destination, --target-file-server=destination-fqdn.

There are also a small amount of changes toward the goal of getting all scripts/*.rb files passing rubocop checks (#26 (closed)). Some for ... in enumeration loops have been changed to the more idiomatic enumeration.each do |...| grammar.

Please do not expect this MR to address all rubocop violations. There is an issue for addressing rubocop violations. From my experience, getting storage_cleanup.rb up to snuff, it will be a lot of work.