Add grid support to QSP (plus bug fixes)

This PR adds support for reading in grid data and weighting the counting of the histogram based on volume of fluid occupied for QSP. This PR also fixes some bugs in the Matlab script.

matlab/spins_QSP_csv.m

-function [T1_max, T1_min, S1_max, S1_min, pdfCount] = spins_QSP_reader(filename)
-  % Reads in the csv file and interprets it in the correct way for the user.
-  %
-  % Input: Filename (string) name of csv file.
-  %
-  % Output: Returns the max/min values for T1 and S1 (as specified in
-  % spins.conf) and the (normalized) pdfCount histogram.
+function [T1_max, T1_min, S1_max, S1_min, pdfCount] = spins_QSP_csv(filename)
+  %% Reads in the csv file and interprets it in the correct way for the user.
+  %%
+  %% Input:
+  %%    Filename (string): name of csv file.
+  %%
+  %% Output:
+  %%    T1_max (float): upper limit of the maximum-valued bin of T1 tracer
+  %%    T1_min (float): lower limit of the minimum-valued bin of T1 tracer
+  %%    S1_max (float): upper limit of the maximum-valued bin of S1 tracer
+  %%    S1_min (float): lower limit of the minimum-valued bin of S1 tracer
   A = importdata(filename);
   T1_max = A(1, 1);
   T1_min = A(1, 2);
   S1_max = A(1, 3);
   S1_min = A(1, 4);
   pdfCount = A(2:end, :);
-  pdfCount /= sum(sum(pdfCount));
+  pdfCount = pdfCount / sum(sum(pdfCount));
 end