preemptive SJF implementation

resolves issue #42.
thanks to jeremy/ricky's magic functions.
everything is easy.
im kind of sad its so easy. hahaha
i like to break builds
changing constructor so it doesnt use quantum time

doesnt need quantum time here
missed a couple of file name changes in gantt and utilities
Merge pull request #52 from rsingla92/Preemptive-SJF

preemptive SJF implementation