Consistent styling for toolbar buttons.

All the different looks here didn't seem to convey anything useful to me, and
looked sloppy.  I went with the style of the transport button.

It would be nice if we could style button elements like Inset in the
configuration, but this would require some work.
Shrink minimum width a bit by using the same hpad for all toolbar selectors.

30 was already being used for some, and looks like more than enough padding,
for me.  Hopefully is enough everywhere.