Modernize Gapminders (#385)

* axes are static and better cell descriptions

* changed thumbnail

* Made edits to cell descriptions

Co-authored-by: Andrew <15331990+ahuang11@users.noreply.github.com>

* updated yml file and moved altair and plotly to different rows

* change data download to the anaconda-project.yml instead of notebook

* added test data files

* deleted data folder

* minor changes to lock file, notebook, and testdata

* Updated the url of dataset

* update some text and headings and display full app in notebook

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Co-authored-by: Andrew <15331990+ahuang11@users.noreply.github.com>
Co-authored-by: Demetris Roumis <roumis.d@gmail.com>