Fix parallel version

Modifications:
Particle -> particles.Particle or particles.ParticleFull
ChargeConservingAreaWeighting -> ChargeConservingCIC
InterpolatorAlgorithm -> CloudInCell
YeeSolver -> SimpleSolver
Implement clone() for FieldSolver and SimpleSolver.

The use of reflection is avoided in this way.
Also clone timeStep.
remove obsolete comment about YeeSolver
Merge pull request #60 from aipp/fixapplet

Avoids using reflection in the applet version.
Merge pull request #62 from aipp/fixparallelversion

Fixed the parallel version by the following modifications:
Particle -> particles.Particle or particles.ParticleFull
ChargeConservingAreaWeighting -> ChargeConservingCIC
InterpolatorAlgorithm -> CloudInCell
YeeSolver -> SimpleSolver