Last four buttons display incorrectly on HiDPI

[mabelzhang]

Since we are fixing issues... I thought I might as well add another :) Saw it while reviewing PRs.

There is something different about how the last 4 buttons in the GUI are created, that makes them display differently from the other buttons. The size is wrong, and the icons on them simply don't show up.

This is the first thing that comes up upon running rqt_bag, so it's super noticeable.
I assume it has to do with HiDPI displays, since on the Wiki page, the screenshots look normal.

To reproduce, on a HiDPI display:

$ rosrun rqt_bag rqt_bag

Notice how the last 4 buttons are very large and blank:

If I do this trick, which is an environment variable that tells Qt to rescale windows and make them appear more normal on a HiDPI display, then the button sizes are right, but they are still blank (icons don't show up):

$ export QT_AUTO_SCREEN_SCALE_FACTOR=1

Not sure if this counts as enhancement or bug.