Notebooker

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* Feature: Flag to preserve original working directory when running notebooks to make local imports and relative paths work.

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* Bugfix: Folders with spaces in their names are now correctly handled in the webapp.
* Chore: Fix readthedocs build and broken CircleCI link.
* Chore: Applying & enforcing Black and Prettier to Python and JS code, respectively. Setting Black version to 22.8.0 for CircleCI.
* Bugfix: Preserve the "mailfrom" parameter on notebook rerun.

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* Feature: GridFS document storage in Mongo-backed instances is now sharded if the mongo server supports it.
* Bugfix: None will stop appearing at the top of reports with nbconvert>7.0.0

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* Feature: Reports are now grouped by their containing folder on the main UI.
* Feature: Allow configuring error email addresses and email subject via UI.
* Bugfix: . and .. should now be allowed to be used when specifying the templates directory.
* Bugfix: corrected cron schedule incorrectly shifting back one day upon save.

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* Feature: A new `--readonly-mode` is available for the webapp. This allows users to have an instance of Notebooker which only displays the results of externally-run or scheduler-run reports. See [the docs](https://notebooker.readthedocs.io/en/latest/webapp/webapp.html#read-only-mode) for more details.
* Bugfix: Scheduler-executed reports will now correctly record stdout.
* Bugfix: Pull from current upstream instead of hard-coded origin/master in git backend of webapp.
* Bugfix: Ensure that the hide_code option is consistent when a rerun is executed via the webapp.

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* Feature: Added support for [Reveal.js](https://revealjs.com/) notebook outputs
* Bugfix: Small bugfix for synchronous report execution
* Improvement: Delete functionality in mongo now also deletes files from GridFS