NH-3573  - Added query cache statistics in MultiCriteria, and cache put only if enabled

Added query cache statistics when using MultiCriteria, and putting to cache only when put is enabled. 

Statistics handling is based on code from Loader.cs.

This fix can be easly backported to 3.x, could that happen?
I believe that I looked at code in NHibernate.Loader.Loader.LoaderPutResultInQueryCache, where the same check is made. It makes sense: CacheMode enum have separate values to allow getting and putting values from/to cache, so when someone only enabled CacheMode.Get without CacheMode.Put, the cache should not be updated.

Now I see that also NHibernate.Impl.MultiQueryImpl.ListUsingQueryCache does not do that check. I should create another pull request for that, but probably at the time when I created this one I didn't notice that