Arrows to GUI; Clean Up Pie Graph plots (Misc)

-Added nice arrow graphics to the main GUI
-Made System Spec pie graphs lump small pieces together (<1% of max
value)
-Cleaned up reactor code
MRE Model Update (v4.2); Browse Button Update

- Update MRE model runner (in the system model) to new format
- Updated MRE excel model to [Version 4.2]
- Added functionality to many of the browse buttons in the system model