* adds Open Humans connection (incl. at least some tests)
* removes the capability to add fitbit data (was broken in any case)
* display current fitbit data is still included, will be removed after grace period (needs to be announced to users)
* Passwords now need to be 8 characters long (new default in authlogic).
* To login to the Sidekiq web interface, log in to opensnp.org, if you
have the `admin` flag set, you will find it at the usual place.
* I finally found out why Rubocop didn't complain about the frozen string literal pragma missing and added all of them.
* Rubocop complained about keyword arguments, which is only relevant for Rails 5, so I disabled the cop.
* I removed the `inherit_from: .rubocop_todo.yml` from `.rubocop.yml`, so Hound does complain about **all** the issues. I also added a few tasks for running Rubocop.
* Remove counter columns
The equivalent operations take less then a millisecond, no need for
trying to keep counters up-to-date.
* Add `with_number_of_users` to Phenotype
* Use `number_of_users` instead of `user_phenotypes.length`
* Improve test
