inspector: Remove a stray separator
inspector: Cosmetics

Add .image-button to the tool buttons in the CSS editor - still
not square.
GtkToolButton: Apply expected button style classes

Add .image-button or .text-button to the button within,
so our css works as expected for toolbar buttons too.
Adwaita: finally kill the scrollbar junction frame...

See https://bugzilla.gnome.org/show_bug.cgi?id=737981