Rails 4 upgrade - try 3 (with a brand new clone of the HEAD of versapay/active_sanity repo)

1) Upgraded to rails 4 (now requires a minimum of ruby 1.9.3)
2) Uses 'find_in_batches' to not choke on tables that might have millions of records.
3) Slight performance tweak by not rerunning validations for the 'InvalidRecord' model since it is run in the first step.
4) Added rubocop settings file and fixed all errors reported by it. To rerun this, use the command: 'rubocop -D --autocorrect'
I am not convinced that using `find_in_batches` and sleeping 50 seconds for garbage collection helps preventing memory overflow. I would rather roll-back to using `find_each` with a batch size of 100 (instead of 1000 by default).