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
Merge pull request #78 from dgelfand/master

Initial conditions grid step independent.