Created interface for particle loader classes
Added method parameters
Added Maxwellian particle loader (not quite ready yet, not tested)
Added temperature parameter and related methods
Corrected return value
Changed error in placemend of ions
Added cutoff (i.e. maximal speed) for the Maxwell distribution and FIXED CHARGE ASSIGNMENT
Turned Particle into an abstract class and implemented ParticleFull which now has the same function as the old Particle.
Cleared anstract Particle class.
Rearanged setters.
Written a flexible particle loader interface and added a few distribution functions.
Merged upstream.

Conflicts:
	pixi/src/main/java/org/openpixi/pixi/physics/Particle.java
Moved particle related classes to one package.
Fixed particle creation in unit tests.
Enabled the particle loader in the settings class.
Generalized some variables and made GUI use the old particle loading method again.
Changed fallback behaviour to the new particle loader.
Fixed typo
Added some comments.
Added some more coments.