Updated so that the code compiles again.

* Updated code to work with latest version of the matrix library.
* Fixed issues with outdated material-data code.
* Added comments to multiple files.
* Removed unused code (mostly from integrate.c).
* Reorganized code (somewhat).
* Updated heat-gui.c and the cooresponding solver.cpp file so that they
        store composition data in an appropriate data structure.
* Made changes to the console version of the can sterilization model to
        make it compile. (It still doesn't run correctly, though.)
* Updated the old Makefile so that it works again.