Use milliseconds for timing.

.../main/java/org/briarproject/bramble/api/system/Clock.java

...c/test/java/org/briarproject/bramble/test/ArrayClock.java

...est/java/org/briarproject/bramble/test/SettableClock.java

.../java/org/briarproject/bramble/io/TimeoutInputStream.java

.../java/org/briarproject/bramble/io/TimeoutMonitorImpl.java

...ain/java/org/briarproject/bramble/system/SystemClock.java

...st/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

...a/org/briarproject/bramble/io/TimeoutInputStreamTest.java