Remove direct output to file from GUI.
Move parts of Particle2DPanel to new class SimulationAnimation.

Particle2DPanel only deals with the graphical output.

SimulationAnimation deals with the animation logics.
Create new class PhaseSpacePanel.

This panel shows graphically the one-dimensional phase space (x vs. vx).
Merge branch 'upstream' into graphicspanel

Fixes a critical bug.
Use JSplitPane.

The split pane is used to separate the particlePanel from the phaseSpacePanel.
use JSplitPane with continuous layout.
Merge pull request #76 from aipp/graphicspanel

Add second panel for graphical display of phase space