* state-db: Print warning when using large pruning window on RocksDb

This pr changes state-db to print a warning when using a large pruning window and running with a
database that isn't supporting ref-counting like RocksDb. This makes the user aware of potential out
of memory errors because this option together with RocksDb etc puts the entire pruning window into
memory. Besides that the pr introduces `LOG_TARGET` for having the target declared central!

* Review comments