[Spike] Self join assembly

- did `rails generate scaffold assembly title:string parent:references`
- edited the app/models/assembly.rb to  `belongs_to :parent, class_name: "Assembly"`
- `rake db:rollback`
- modified the migration to be:  `t.references :parent, index: true, foreign_key: "parent_id"`
- `rake db:migrate`
- Couldn't find helper method find_by_parent_id for some reason.
- added the route by hand