Small refactor to simplify households_controller
README update
Bundle state machine
Add state column to completables and migrate
Add state machine definition to completable

and refactor away the methods replaced by state transitions
rename completable.pending "state" to 'active' state
README update
readme update
add target to events table
Create base event model and some subclasses
Create events when todos are accepted or completed

Also refactor the way todo state transitions pass arguments