Forcing path override

[JordanLaserGit]

Problem: Users frequently run into problems properly setting paths within the realization file while using NGIAB.

Solution: Assuming a standard directory structure is enforced as outlined here: #17 , NGIAB should override the forcing path parameter with which ever is finds in the data directory. Same for the forcing file pattern. These two parameters are useful for ngen in other contexts, but it's a source of annoyance for NGIAB users.