Support 80 column terminals in change view

The change view has assumed a very wide display.  Use a gridflow
widget to achieve a similar layout on wide displays but fold the
right-hand side data underneath in 80 column displays.

Technically, the change info, commit message, and votes sections
go into N 80-char columns depending on how wide the display is.

Change-Id: I0d55a8a51c0d918e608b892e94cf9cb38d2b3547