Files: removed, as it actually only served for string utilities.
Duration: added await() and awaitUninterruptibly() methods.
Duration: softSleep() -> sleepUninterruptibly() for consistency.
Duration: timedWait(), timedJoin() -> wait(), join() since the time is implicit.
Duration: moved to the ch.usi.dag.util package in src-util.
Job: remove duplicated __streamToString() and use Strings.drainStream() instead.
Job: use the generic awaitUninterruptibly() in waitFor().
src-test: reflect the above method and class movement.