Fix: when using page cache in store migration or tools make sure the sweeping thread is running

I dislike these manual `init()` and `start()`, and the fact that you return a PageCache out for which you cannot really stop the sweeper thread. I would like to have the `StandalonePageCacheFactory` perhaps be renamed and be something implementing AutoCloseable, where the page cache is created in the constructor, lifecycled page cache tucked away and `close()` closes it.