Rename methods for adding comments

* I have a feature branch that implements issue commenting. This commit
  renames methods in `PullRequest` and `GithubApi` in anticipation of the
  changes on my branch.
* Rename `PullRequest#add_comment` to `PullRequest#comment_on_violation`
* Rename `GithubApi#add_comment` to `GithubApi#add_pull_request_comment`
Access owner information from PullRequest
Custom thoughtbot configuration for rubocop
thoughtbot specific config for Coffeescript
Refactor default_configuration

Have base class handle logic behind thoughtbot default config vs hound
default config
thoughtbot specific config for JS linting
Refactor configuration loading in specs into helper