MPI types are now freed
freed cells in universe dictionary after its use in initialize
converted manual linked list for energy grid to linked list type from list header which allows it to be easily freed
Change list insert method to be compatible with get_item's last_elem pointer, and take advantage of sequential inserts
Set prev pointers in list_remove.
size method now used to determine the size of the linked list for unionized energy grid
Merge branch 'develop' into clean
Merge pull request #207 from mit-crpg/clean

Fix Memory leaks from Valgrind