Tweak default toolbar to fit View Mode combobox

This is a useful UI element that I find myself using a lot, so quick
access is helpful. Another person just submitted a similar change (see
!689) so it would seem there is some demand for this.

In its current form, the toolbar contents would be too long if we added
it, and items would get pushed into the overflow menu. To prevent this,
let's also drop the separator lines and text from the zoom buttons.