Resubmit: remember column widths, fixed for receive modes

I think this is working ok now. I tested it in various ways with receive modes, exiting and starting again. Now it saves col widths between mode switches and saves distinct widths for each receive mode view.

Cavaet from past testing: If you tested the last version it will have saved a column-widths array in your config that will break upon loading now. This is because the new format includes 3 arrays for the receive tab. I didn't want to clutter the client with code to detect and fix that since only 1 or 2 people (who may have tested the last col-widths version) will have the issue. If you get an exception on first start with this code then it means your wallet has a broken column-widths value. The simple temporary fix is to force it to use defaults on line 330 in gui_qt.py just for the first run. After that, undo and run again as config will now have new values.