shuffle label

shufflelabel randomly changes the order of label values in a label matrix. Zeros and nans are ignored. The label matrix can be every numerical data type, char or a cell array of strings.
 
 
 Example
  
      L = kron([1 2 3;3 2 3],[1 1; 2 2])
  
  
      L =
  
           1 1 2 2 3 3
           2 2 4 4 6 6
           3 3 2 2 3 3
           6 6 4 4 6 6
  
      Ls = shufflelabel(L)
  
      Ls =
  
           3 3 6 6 1 1
           6 6 2 2 4 4
           1 1 6 6 1 1
           4 4 2 2 4 4

fixed helpblock, added a reset option