Fix SimulatorTimer-related bug in EclipseWriter.

Since writeTimeStep() now gets called also before the first timestep is done,
the EclipseWellTotal::update() method was in error, always calling
SimulatorTimer::stepLengthTaken(). That method cannot be called if the
timer's currentStepNum() is 0, so that is checked for and intercepted.
The total rate in that case is of course zero.
Fix initialisation warning.
Suppress warnings in unimplemented functions.

This prevents warnings from functions that are right now just
a throw statement. Also cleaned up a few whitespace issues nearby.
Moved explicit template instantiation inside namespace.

Clang requires this to happen inside the namespace of the class
(which is in the anonymous namespace) and issues an error diagnostic.
Suppressed some unused parameter warnings.
Removed unused argument from buildTracerHeadsFromWells().
Fix unused argument warnings.
Fix variable shadowing warning.
Fix unused argument warning and wrong behaviour.

The class WarnAndContinueOnError should write warnings irrespective
of the status of the OPM_VERBOSE symbol.
Merge pull request #488 from atgeirr/fix-eclipsewriter-for-clang

Fix eclipsewriter for clang
Merge pull request #485 from atgeirr/fix-initial-call-eclipsewriter

Fix SimulatorTimer-related bug in EclipseWriter.
Merge pull request #487 from atgeirr/fix-warnings

Fix some warnings
Merge pull request #489 from atgeirr/fix-more-warnings

Fix more warnings found by clang