Documentation Fixes and Edits

[johnthagen]

• Remove unused imports in example code in tutorial
• Set AUTH_USER_MODEL properly in settings to avoid error on migration
• Move tutorial further up in the user guide to make it more accessible for new users
• Fix many typos

[johnthagen]

@hishnash This MR is ready for review. I will have some follow up questions/issues but that can be handled in a separate issue.

I made each commit separate so that you can look at them in isolation, but this PR should probably be squashed when merged.

[johnthagen]

I found some other issues that blocked me from completing the tutorial, but that will be deferred to:

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