Merge pull request #75 from dgelfand/master

Output extended, two-stream instability implemented.
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).
Fix bug "array index out of bounds"

Index stays within grid size.

Patch by Clemens Müllner.
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.
Move panels to new package ui.panel.

This includes:
- Particle2DPanel
- PhaseSpacePanel
Add ElectricFieldPanel.

This panel shows the one-dimensional electric field along the x-direction.
Several field lines for various grid positions along the y-direction are
superimposed.
Change panels by right-clicking on them.
Merge pull request #76 from aipp/graphicspanel

Add second panel for graphical display of phase space
Merge pull request #77 from aipp/electricfield

Add new panel to display the electric field
Initial conditions are now largely independent off the chosen grid step, this was achieved by considering charge density instead of charge in the FFT routine by getting sure that each charge is treated like a uniformly charged rectangle of the size of an elementary cell. For this purpose measurement of snapshot files has been added, now we can do 3D plots of some grid quantities.
Merge with master, minor manual changes were needed.

Conflicts:
	pixi/src/main/java/org/openpixi/pixi/ui/Particle2DPanel.java