Adding 2D grid capabilities for SRH calculation #1258

I am wanting to use the storm-relative helicity calculation routine to plot spatial maps of SRH using WRF output. Right now the function is written such that it only works with one data point at a time. The biggest hangup that I have found with trying to amend the code seems to come from the layer extraction routine for the Bunkers storm motion (and the layered dependencies of the SRH function on multiple upstream functions). Then, the SRH function requires individual values for c_u and c_v instead of 2D arrays.

I tried to just write a for loop to loop through each point in x,y and then calculate the SRH that way. It works in principle but is incredibly inefficient (taking hours to calculate for each time). I realize that there is an option to calculate 2D SRH fields through WRF-python, but this seems to give me unreasonably large values.