feat: simplified user administration

[NanamiNakano]

No description provided.

[forrestbao]

Can we make user administration as simple as below?

1. Add a dummy, empty CSV file with the correct columns.
2. To add, delete, or update users, just edit the CSV file.
3. When done, use one command to convert CSV to SQLite file.

The script for user administration shall be called use_admin.py It shall have to subcommands: csv2sqlite and sqlite2csv.

Tell the admin to put the CSV file in a safe place.

[NanamiNakano]

I think I've simplified this far, except for not renaming the file. I added the documentation for the new script in the Readme. Or am I not understanding what you are saying?

[forrestbao]

For all actions other than creating a new user, there should be a one-to-one correspondence between the CSV and the SQLite DB. Thus, the content in CSV shall be the same as the content in the SQLite DB.

As an example, to delete a user, simply remove the row in the CSV file corresponding to that row and import (called "apply" here) to the SQLite folder.

Let me work on user admin. I feel mixing command line options and CSV file makes it complicated.

[forrestbao]

@NanamiNakano I have refactored the code to avoid using the CSV as an importing source. The user admin script has been renamed from user_utils.py to user_admin.py. Please see user_admin.md for the usage and test all options, and fix bugs if needed.

At one place, I used an ugly implementation. Please find it by searching FIXME and fix it.

Third, to avoid confusions, we shall rename user_name to name. Please make the change throughout the codebase and docs.

When done, please submit a review.