Add and configure 'sidekiq' gem for queuing jobs

This queue is backed by redis.
Add a redis-backed volatile lock

This code is useful when:
* a batch job is configured on several (identical) nodes
* it only needs to run once

This code was originally taken from 'alphagov/signonotron2' and lived
in the 'support' app.
Add and configure webmock

This allows stubbing out and asserting on calls to remote dependencies.
Add 'factory_girl'

This provides a handy DSL for dealing with constructing models with various defaults.
Add and configure 'gds-api-adapters'

This is required for publishing metrics to the Performance Platform.
Calculate aggregate metrics for service feedback

User satisfaction ratings, which is part of the service feedback,
is used to calculate a user satisfaction score for each service.
Add worker for uploading to the Performance Platform

There's one job per worker, per day. This is so that if the dataset for
a particular service doesn't exist yet (as the service is new), then
the metrics for the other services upload without a problem, and the upload
for the new service is retried repeatedly (by sidekiq) until it succeeds or reaches
the maximum number of retries.
Add rake task which handles the batch upload of service feedback

This handles:
* triggering the 'sidekiq' workers
* handling the locking (so that the same batch isn't done multiple
times across different nodes)
Add 'whenever' library for scheduling batch tasks
Make feedback queries default to actionable-only

There aren't really any cases where it's useful to return non-actionable
feedback (eg spam or duplicates).
Add Foreman configuration for 'sidekiq' queue