Fixed error in CMFD computeDs and increased segmentation Performance

- Fixed error in CMFD computeDs method.
- Changed convergence to be based on FSR energy-integrated fission source.
- Increased segmentation performance by looping on over the surfaces in the current cell (instead of all surfaces for all cells in the current universe) to check for next surface crossing.
- Changed FSR keys map from `map` to `unordered_map`. The `unordered_map` scales as O(1) whereas `map` scales as O(log(n)) so the `unordered_map` is needed for large problems. 
The cuda compiler does not have support for unordered maps, so we have to tell the cuda compiler to ignore code that uses unordered maps. The GPU code uses the CPU and C++ code for segmentation and manipulating the fsr keys unordered map, so this should not affect anything with the GPU solver. With this modification the cuda code compiled and ran fine on Smithwick.