Add option to start bot without db

[wizzdom]

Add either an envvar or commandline argument to start the bot without the database.
This should make it easier to test the bot locally when the database isn't being used.

[novanai]

An idea: write a decorator for commands which marks them as requiring the DB, then stop the bot from registering these commands on startup.

e.g. instead of using the usual @plugin.include hook, write a custom one which will not register the command if it requires the db and the bot is being run without the db.