Class to install redis gem

The sidekick monitor needs the redis gem to do it's thing,  add a class
to install it, in the same pattern as the mysql one.
Fix class comment
Class to load sidekiq gem

the sidekiq monitor also requires this gem to do it's thing.
Default version of gem to use

The sidekiq scout plugin doesn't appear to work with the current (3.2.x)
version of the sidekiq gem.  Given SSO uses 2.8.0 default to using this
as well.
Merge pull request #7 from envato/scout-redis-gem

Scout redis gem