Migrate all examples to use Globus SDK Apps, and remove "Hub" tokens.

[NickolausDS]

Currently, most or all notebooks contained within this repo implement auth "manually" for requesting Globus tokens, which includes listing scopes, starting auth flows, and optionally saving tokens. All of these things can be streamlined with the use of Globus Apps, which both have the benefit of simplifying the code in each notebook and giving users best practices for how to interact with the Globus API.

Additionally, many notebooks use "Hub" tokens, which involves logging in through jupyter.demo.globus.org and using tokens provided in the GLOBUS_DATA environment variable. While useful in the past, this isn't the clearest demonstration of the authorization code grant and additionally complicates auth process with a separate check for "Hub" tokens in each notebook. This should be removed in favor of using the Globus Apps above.

We'll need to update the following notebooks:

• Auth_App_v_Human.ipynb
• Automation_Using_Flows_With_Search.ipynb
• Automation_Using_Globus_Flows.ipynb
• Compute_Introduction.ipynb
• Data_Distribution.ipynb
• Flow_with_Compute.ipynb
• Gladier_Flows_Tutorial.ipynb
• Groups.ipynb
• JupyterHub_Integration.ipynb
• Metadata_Search_and_Discovery.ipynb
• Platform_Introduction.ipynb
• Transfer_API_Exercises.ipynb