Navbar: let the left and right parts absorb free space
Navbar: let the left and right parts absorb free space

Previously, we had the width of those pieces fixed, undersizing would
result in wrapping. Now they can grow as needed and absorb the extra
space.

They start at the same default width (which keeps the title centered)
and then grow equally to fill all the space. Upon geting smaller, we let
only the search field shrink.

iFixit/pulldasher,iFixit/pulldasher,iFixit/pulldasher,iFixit/pulldasher