Consolidate UriHandler commands

[sourishkrout]

We currently have setup & demo. Where the latter assumes repo are already checked out and if so will open a markdown notebook in the respective repo, scroll to the cell, and run it.

1. Let's leave setup untouched.
2. Introduce a new command called run that, if possible, checks if the repo is already available (checkout path convention) or checks it out before opening the notebook and running the cell.
3. Let's have demo become an alias of run just so we don't have to change all existing references.