bnc#904423: Text(box) is rendered white on white when it is not

The problem was that the background color defined by theme
was not imported correctly, because the different fill
style comes from different sources (master slide, theme,
direct formatting) were applied on the shape in wrong order.

To solve this we need to store master slide defined fill style
in a different variable so theme style can be applied after master
slide defined style but before direct formatting.

Change-Id: I99ea981858b9fa391915570187c8ddfdf2be1f7a