..logbook: adding level support

Change-Id: Icf376dd36fec704158dccac0fa709f4db16d691a
..LogEntryWidget: fixing the logEntry update mechanism to only queue the
last logEntry.

Change-Id: I2a46f9f2d892ce6f033e7b123faff81133e62ed1
Merge branch '3.2.x' into logbook
Merge branch 'logbook' into 3.2.x
Merge branch '3.2.x' of ssh://git@github.com/ControlSystemStudio/cs-studio.git into 3.2.x