User Task

### Description
It would be nice if we allowed users to create tasks through Grace, like a personal `TO-DO` list for each user. The feature would allow users to `list`, `add`, `delete`, and mark tasks as `done` through Discord commands.

The tasks added by the user should persist even after reloading the bot. We could store the data in the database, and potentially have a command to list every task terminated. This command could be something such as `/archived`, and it will list everything the users have completed.

The information that Grace gives back to the user should be displayed in an embed, not in plain text.

### Additional context

See https://github.com/Code-Society-Lab/grace-framework/wiki/Getting-Started#adding-commands for more info.

If any questions, feel free to ask in the comments below or ping `Astra` or `Malassi` on Discord.