Revamp Doctor Checks

[ethankhall]

Based on some feedback, updating the doctor models to be easier to work with.

• [x] Create ScopeDoctorGroup model, automatically translate Setup and Check to this model.
• [x] Validate a check passes after a fix before moving forward.
• [x] Add a "required" concept, allowing the user to define if an action is required, defaulting to requires.
• [ ] Add "needs" concept to the group, to describe ordering of groups.
• [x] Add "help text" and "url" to the "fix" section of an action.
• [ ] Add ability to prepend paths to PATH for a group.