[improvement] define roles per project rather than globally
[refactor] add project_id to TestingNote
[refactor] add project_id to Commit
[refactor] add project_id to Change
[improvement] make authorization more fine-grained: per project
[skip] by default, do use letter_opener in development
[skip] don't validate uniqueness of ticket number if it's nil
[skip] don't attempt (and fail) to create local tickets for Null objects