Migrate the repo to `pallets-eco/flask-debugtoolbar`

[jeffwidman]

We're migrating the location of this repo from flask-debugtoolbar/flask-debugtoolbar to pallets-eco/flask-debugtoolbar to co-locate it alongside a number of other popular Flask-related extensions.

In order to complete this migration, we need to do a few things:

• [x] transfer the repository to the pallets-eco org
• [x] Make myself & @nickjj repo admins - this needs @davidism
• [x] Make @mattaw a repo collaborator - I think I can do this once @davidism adds him to the pallets-eco org
• [x] Make @davidism and @ThiefMaster owners on https://pypi.org/project/Flask-DebugToolbar/ in case we ever need to publish an immediate security update or something more trusted users have access- I just sent them invites
• [x] Update outdated links to mgood/flask-debugtoolbar or flask-debugtoolbar/flask-debugtoolbar to point to pallets-eco/flask-debugtoolbar instead... I currently see some in https://github.com/pallets-eco/flask-debugtoolbar/blob/master/docs/index.rst and https://github.com/pallets-eco/flask-debugtoolbar/blob/master/setup.cfg
• [ ] Cut a new release of flask-debugtoolbar and push to PyPI so that the project metadata on https://pypi.org/project/Flask-DebugToolbar/ points to the correct URLs.

[jeffwidman]

All of this has been done except for cutting a new release, which will happen inevitably whenever a new release happens... currently that's also tracked under #192 , so I'm closing this as done from the code/access rights side.