Vector should be explicitly included

Previous builds always included this through the pre-compiled headers,
which obviously is not available in every toolchain.
Use argument names that doesn't conflict with methods

The compiler may generate a warning for this, although there shouldn't
be any ambiguity about which symbol that is actually used.
Use the new Event scheme from opm-core
Depend only lightly on iostream library

The dump code which uses streams is only activated when debugging;
don't penalize the build by always pulling in the entire thing.