Sklearn-evaluation

- Updates telemetry

- Adds [plot.ConfusionMatrix]{.title-ref}

- Updates telemetry key

- `NotebookDatabase`: makes `path` the primary key
- `NotebookDatabase`: `.index()` uses path to see if the notebook has
been indexed
- `NotebookDatabase`: adds `update` to `.index()`

- Adds anonymous telemetry

- Query notebooks with SQL using `NotebookDatabase`
- Stripping output string in `NotebookIntrospector`
- Ignoring standard error output in `NotebookIntrospector`