Use log4j inside h2o now.

This replaces the bottom-level file access.  The calls to h2o logging
api throughout the code are unchanged.

This gives us a few capaabilities for free:
-  persistence on restart
-  rotation
-  space management
Convert distributed log file collection to distributed log directory collection.
Merge branch 'master' into tomk-log
Add ip address to node log file name.
Read log file shown in the web browser from disk.
Put top level files in a directory.
Tweak log file stem name to include full year.
Change dashes to underscores, so underscores are consistent throughout.
Merge branch 'master' into tomk-log

Conflicts:
	src/main/java/water/api/LogView.java