StyleItem: Fetch fonts from platform theme
StyleItem: Fetch fonts from platform theme

Not complete, but covers the fundamentals.

Change-Id: I30ed19240dbbc38a69cc04a639f43c21078cafa3
Reviewed-by: Jens Bache-Wiig <9cea9d70b08f8210134ec5959114f72bad51ed1d@digia.com>

drgvond/qtquickcontrols,jfaust/qtquickcontrols,drgvond/qtquickcontrols,richardmg/qtcomponents,mizukusak/qtquickcontrols,richardmg/qtcomponents,drgvond/qtquickcontrols,jfaust/qtquickcontrols,jfaust/qtquickcontrols,mizukusak/qtquickcontrols,kobolabs/qtquickcontrols,mizukusak/qtquickcontrols,richardmg/qtcomponents,kobolabs/qtquickcontrols,kobolabs/qtquickcontrols