Added option to selectively save files.

Hi,

Been fiddling around with ImvInv again.

I have added some options to choose which files you can save. I was finding I was waiting a lot for my files to be saved out before I could try another centre for inversion.

I have added extra settings options and a save menu item. You choose files to be saved using checkboxes in settings menu. Then saving is similar to before using File-->Save-->Selected menu.

Ciarán