Build 304D is released.

1. Added additional diagnostics for the Input\Output files presence during the N4 execution.
2. BiCal dialog: Changed the Subsample parameter to Processing Scale parameter [0.1,10]. Fixed the defects and tested. Note: now the larger number will slow down processing, smaller will speed up.
3. Substantial BiCal speedup when using Processing Scale = 0.5. On 7T brain a minor reduction in quality with NU raising from 0.051 -> 0.057
4. BiCal: Speedup in matrix construction