Update how commits are found for a project (uses repos now)

Here are the routes:

```
               Prefix Verb URI Pattern                                        Controller#Action
api_v1_project_commits GET  /api/v1/projects/:project_id/commits(.:format)     api/v1/commits#index
 api_v1_project_commit GET  /api/v1/projects/:project_id/commits/:id(.:format) api/v1/commits#show
  api_v1_project_repos GET  /api/v1/projects/:project_id/repos(.:format)       api/v1/repos#index
                       POST /api/v1/projects/:project_id/repos(.:format)       api/v1/repos#create
   api_v1_project_repo GET  /api/v1/projects/:project_id/repos/:id(.:format)   api/v1/repos#show
       api_v1_projects GET  /api/v1/projects(.:format)                         api/v1/projects#index
                       POST /api/v1/projects(.:format)                         api/v1/projects#create
        api_v1_project GET  /api/v1/projects/:id(.:format)                     api/v1/projects#show
   api_v1_repo_commits POST /api/v1/repos/:repo_id/commits(.:format)           api/v1/commits#create
           api_v1_repo GET  /api/v1/repos/:id(.:format)                        api/v1/repos#show
```