Revert "Upgrade RuboCop to 0.23.0"

This reverts commit 1e3e4200579fd567a53b417f15776c98d1e2650d.

Rubocop has changed their configuration structure which will break existing
config for all of our users. Until we find a strategy to deal with this, we
should not upgrade any higher.
Lock RuboCop to v0.22.0

* Update configuration link to point to the right tag of RuboCop
Update configuration.haml

That ain't YAML. This is YAML.
Extract CommentingPolicy policy object

* Extract `CommentingPolicy` object for logic around permitting
  Hound to comment on a line in a pull request
Add Hound logo to home page

* Add Hound SVGs to home page
* Move line on homepage to the left
* Remove old hound image

https://trello.com/c/U2GJGKlo
Merge pull request #286 from bhardin/patch-1

Update configuration.haml
Clean up Commenter and CommentingPolicy specs

* Remove specs testing logic currently tested in `CommentingPolicy`
  specs from `Commenter`
* Don't stub unused and nonexistent methods in `CommentingPolicy` specs
WIP, don't duplicate comments after force push