- BUGS
  1- After fitting, the fit panel is not updated with the output values of the fit.
  2- Do this:
      a) load a file
      b) fit a straight line
      c) change the scale using the "Properties" menu. 
      You will see an exception that should be fixed.

  3- Load the file line_in_x2_y.txt in miniView. Select x^2 and y for the scales. Fit it. 
      a) The fit range is wrong, it's not update for the X^2 view.
      b) the fit result is wrong
      c) Even if you update the range, the fit and the plots are wrong.
      
- NOTES that might help for bugs
  1- Make sure you are fitting the View data, not the underlying data
  2- Since you are using the log scale from matplotlib, the fit for when one of 
  		the axis is in log will NOT be a straight line
  3- Make sure that you are filling the View of the fit result correctly.
  

- IMPROVEMENTS
  1- After loading a new file or changing the scale using the "Properties" menu, remove any previously displayed fit from the graph.
  
  2- There are additional y scales we need: y, y^2, log(y), 1/y, 1/sqrt(y), log(y * x), log(y * x^2)
  3- You should change the label according to what the user chose, and not hard-code them.
     For example, in PlotPanel._onEVT_FUNC_PROPERTY, replace
          
            self.graph.xaxis('\\rm{q^{2}} ', 'A^{-2}')
         
         with
            name, units = self.some_plottable.get_xaxis()
            self.graph.xaxis("(%s)^2" % name,  "(%s)^2" % units)
    
     That way it still works even if the user is not plotting Intensity versus Q.