Redoing Logging to Make it Less Stupid

And by that I really do mean REDOING it! We now have a more sane
logging architecture; things can be tagged, syslog works as expected,
the tagged logger is better...

Really what I did though was move signifcant parts of Logger.php
into LogContextHandler. This allows detaching of context
objects for things like hooks or raw data loggers.

I also abstracted the concept of a 'log event' into LogEvent which
stole some further code from Logger.php.

RawDataLogStream became the TaggedLogger (eventually we will probably
need a generic InstantiableLogger and ILogger symphony thing.)

The log streams got moved into /LogStreams because they were getting
in the way.

And everything was updated to use the new stuff.

Change-Id: Idf1db578fa32531ce7dab7abc2c3aa7910dc1971