Merge pull request #74 from dgelfand/master

Request to add changes made by Clemens90 and implemented by him and myself to the master branch.
Move OpenCL tests to separate directory.
Deactivate further tests that currently do not work.
Remove duplicate call.
Fix bug for initial conditions of pair:
The problem was in MainControlApplet.setSlidersValue():
after initialization of Simulation, it called particlePanel.s.grid.changeSize(...) which reset the grid.

Because the ConstantForce was not linked, actually setSlidersValue() crashed when
force.ex was called, so that changeSize(...) was not called in that case.

After removing changeSize(...), it correctly works also with additional ConstantForce.
Fix bug: in MainControlApplet.setSlidersValue() set slider value
according to current setting in simulation.

Previously the time step was hardcoded to 0.5.
Move OpenCL code portions to separate directory pixi_opencl
Update directory structure in pixi_opencl.
(files have only been moved, not modified)
Two-stream instability implemented, output extended such that spectrum files are created after certain periods of time, controlled by a new variable specstep. Eps_0 constant in PoissonSolverFFTPeriodic changed in order to be consistent with the field dynamics.
Merge https://github.com/openpixi/openpixi into upstream

Conflicts:
	pixi/src/test/java/org/openpixi/pixi/parallel/ParallelSimulationTest.java