CC3D Code Beautification :)

Main Python File
- Renamed Condensing -> Stem
- Renamed NonCondensing -> NonStem

Steppables
- Moved all "import" commands to the top
- Deleted some unnecessary code
- Added a lot of helpful comments
- Enabled all 3 plots: time plot of population by species, histogram of
cell volume by species, and time plot of total cell volume by species
- Renamed dedifferentiation variable from "self.de" to "self.r" to
better variable names in the ODE model
- listSumVolSC/listSumVolNSC/listSumVolDC: list of total volume of each
species at each MCS -> used to plot total cell volume
- volList1/volList2/volList3: list of individual cell volume of each
species at a single MCS -> used to plot the histogram of cell volumes
- Renamed total volume plots to "Total Stem Cell Volume"/"Total NonStem
Cell Volume"/"Total Dead Cell Volume"
- Organized code in a way that is easy to comment/uncomment to
include/exclude functionality