Remove unused test files.
Add RSpec and Capybara for testing.
Basic tests for static pages.
Tests for User model.
Tests for Notebook model.
Allow Notebooks to be associated with many users (but one owner).

This is done through a many-to-many relationship in the database, and
a single `owner` field/column in the Notebook model/table. If we
decide later to have multiple admins for a single Notebook this will
need to change, but this works for now.
Make Notebooks work again with the new schema.

look at me learning rails
Allow users to share notebooks.

Right now some (basic) permissions are enforced, but a better approach
is needed to make sure that only the owner of a notebook can edit its
structure.
Update tests to pass with notebook sharing.
Make notebooks accessible from their constituents.
Prevent users who don't own notebooks from altering them (or seeing
links to allow them to do so).