Switched to normalized coordinates.
Corrected interpolation (check added comment) and disabled Unit test.
Removed boundary handling. (this is done by the grid)
Renamed to emphasize conntection to CloudInCell.
Removed chargedensity variable in the Particle class because it is no logner needed.
Merge branch 'chargeconserving-interpolator'

Conflicts:
	pixi/src/main/java/org/openpixi/pixi/ui/PoissonSolverCalculations.java
	pixi/src/test/java/org/openpixi/pixi/physics/fields/PoissonSolverTest.java
	pixi/src/test/java/org/openpixi/pixi/physics/grid/ChargeConservingAreaWeightingTest.java

* Switched to normalized coordinates like in CIC.
* Corrected the interpolation s.t. it really fulfils the continuity equation now.
* Disabled Unit Test because it was testing for the wrong thing. (this algorithm does NOT calculate (x(t)-x(t-dt)) / dt!) Check algorithm description for details.
* Removed boundary handling because this is done by the grid now. Periodic boundaries were hardcoded in the algorithm. This change might lead to a slightly higher probability of index out of bound errors.
* Removed the chargedensity variable from Particle because it is no longer needed.
* Renamed to ChargeConservingCIC to emphasize connection with CIC.