Make extrapolator private ParticleCaloExtensionTool

In preparation for migrating to the new configuration, I wanted to make the extrapolator private in ParticleCaloExtensionTool. This proved to be a bigger job than expected, because lots of tools and algorithms didn't explictly configure the extrapolator. Not all have been migrated, but this is to give a heads-up to other domains about the changes I am making. Given that the old configuration will hopefully soon go away, I was not being very careful about making the "nicest" changes.