Decouple joomla/log and joomla/filesystem

There's a circular dependency between our Log and Filesystem packages at the moment.  One way to work around this is to have the Filesystem package utilize the Logging PSR instead, which is what this PR does.

With that said, I've been thinking over the last day about this too, and IIRC, the logging statements were for CMS support primarily.  So, another alternative would be to throw exceptions.  Food for thought.