Mimic the behaviour and style of the sugar GTK+ 2 sub-toolbars in GTK+ 3
Mimic the behaviour and style of the sugar GTK+ 2 sub-toolbars in GTK+ 3

This draws the grey line around the toolbutton icon with a gap at the
bottom and a grey line at the top of the subtoolbar. Furthermore it
gets the highlightning of the button correct, in the pressed and hover
state. This patch depends on the sugar-artwork patch with the id
7464b808eb12b1df650952e3c8214acff1d1360f.

Signed-off-by: Gonzalo Odiard <8e43bec6c9a4aba7dc358247a21ab52d301a2840@laptop.org>
Signed-off-by: Manuel Quiñones <6f5069c5b6be23302a13accec56587944be09079@laptop.org>
Acked-by: Simon Schampijer <088e16a1019277b15d58faf0541e11910eb756f6@laptop.org>

tchx84/sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3,gusDuarte/sugar-toolkit-gtk3,gusDuarte/sugar-toolkit-gtk3,manuq/sugar-toolkit-gtk3,tchx84/debian-pkg-sugar-toolkit-gtk3,tchx84/sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,tchx84/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,tchx84/debian-pkg-sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3,manuq/sugar-toolkit-gtk3,gusDuarte/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,gusDuarte/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,tchx84/debian-pkg-sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,quozl/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3,manuq/sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3