Rationalize usage of WorkDir

Right now most objects inside our hierarchy share the Working Directory
configuration parameter which allows us to set the the directory where each
element works. Now this is a nice feature but it may lead to a duplication
of directories and to some confusion about where exactly we are working.
As an instance, we should have actions that work where instructed by the
EventConsumer which usually creates a new dir inside its workdir every time
it receives something; this is done in order to prevent problems of having
different threads working on the same dir with clashing filenames.