bot command: simple command generator

write a cog that will allow for a user to input simple commands directly into the bot.

ex. .addcmd barking-snake
this command would add the command .barking-snake to the bot, when it's run - it shows the given img.

several ways to do this, can be data driven - create a small database that holds command name, command function, and on/off. then use some generic bot logic to catch commands on_message and preform actions when commands are caught.

another option would be to have code _write_ the code using scaffolding - but this might be a bit cumbersome and bloat the codebase.

No file, test, or entry point is named. First determine how the bot currently receives commands and decide between the proposed database-driven approach and code scaffolding. Done means a user can add a simple command such as `.barking-snake` with an image and invoke it successfully.

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