Make script reloading dynamically configurable

[clintongormley]

Re #4062

Not sure if we need two separate settings for script reloading, ie watcher.interval and script.auto_reload_enabled. I'd make it just one: script.auto_reload.interval which defaults to -1.

I'd also like it to be dynamically configurable, so that I can turn it on (with a short interval) while making changes, then turn it off again.

Perhaps we should keep script.auto_reload_enabled and default it to true, but make it non-dynamic, to avoid a potential exploit.

[clintongormley]

Meh, changed my mind. Closing