Reactor outage separate from refueling outage

[nuclearkatie]

It would be nice to model reactor downtime separate from the refueling process. This would be useful for modeling reactors with online refueling or liquid cores, which still shut down for regular maintenance but not every time fuel is moved.It would also be nice for any simulations that care about power records to be able to shut down a reactor for reasons other than refueling or resource scarcity

Might be a feature related to the question posed in #585? I think this is reasonable to add to reactor, but if an effort is made to create a new archetype library for more complex reactor behaviors it could also go there