Add a way to disable auto reload

[yotamN]

Auto reload is great but the way it's implemented it deletes any state in the REPL. I propose to add a flag to disable it.
I personally think auto reload should be off by default but because we can't change it without breaking backwards compatibility I suggest adding the flag --no-auto-reload. If we want to eventually make it the default I also suggest adding --auto-reload flag that does nothing so the migration will be easier in the future.

We should also have a way to change the settings from the REPL which mean a %autoreload {on/off} command.

I plan on implementing it after my magics refactor is merged.