Regression: Added vairables

[GoogleCodeExporter]

Keep the specified XY variables in the regression dialog after the residuals or 
predicted values are added to the table (currently the regression dialog is 
reset to empty, so all the variables in the model specification are gone).  
Also keep the "save to file" button is enabled (it's currently disabled after 
adding residuals or predicted values) -- otherwise users would lose their 
results after adding the variables if they hadn't saved them before. 

Original issue reported on code.google.com by [email protected] on 16 Jul 2015 at 2:00

[GoogleCodeExporter]

This is apparently an old issue, see also #108

Original comment by [email protected] on 20 Jul 2015 at 9:26

[GoogleCodeExporter]

save all models to output file - not just the latest one. 

Windows formatting of regression output is off with different font: columns are 
not aligned. 
Suspect this is due to default font not being picked up?

Original comment by [email protected] on 27 Jul 2015 at 12:32