WIP Assistant / TaskPlans / Sprint 3

Don't merge, WIP.

To test it out, switch to this branch and then run:

```
rake db:drop
rake db:migrate
rake sprint:003
rails server
```

Go to `http://localhost:3001`, sign in as the sole user (printed out in the sprint:003 run above.


mattr_accessor is not thread-safe so if you plan on changing use_stubs during runtime in the future (outside of some config file) I suggest making BigLearn a class, making use_stubs an instance variable and making the method below an instance method.