Add convenience functions and example notebook for datasource CRUD

[aaronxsu]

This PR:

• adds some convenience functions for datasources' CRUD
• adds an example notebook for it

How to test:

• Point to spec in here https://raw.githubusercontent.com/raster-foundry/raster-foundry-api-spec/feature/asu/update-first-class-object-crud-spec/spec/spec.yml
• Run the example notebook

This is the first part of #53

[jisantuc]

What do I need to set my host to when I create the client? localhost:9091 is throwing a swagger validation error, and I need to point to local for the changes in raster-foundry/raster-foundry#4105

[jisantuc]

For user's who've pip installed, this won't be necessary, since pip will have put the library in their path. For users in development, if they've done scripts/update and are in the resulting virtualenv, it also won't be necessary, since that script installs rasterfoundry into the virtualenv. So this cell can be removed.

[aaronxsu]

hey @jisantuc , api = API(refresh_token=refresh_token, host='localhost:9091', scheme='http') has been working for me. Please let me know if it still does not work.

[jisantuc]

Looks good 🎉