Core: Fix "compile error" overlay in progressmanager_win

In order to fit a text into a fixed-sized image, we have to use
pixel sizes for fonts. The default point size can be anything
and the dpi can be anything.

Also, decomplicate the drawText call.

Change-Id: I20da8177a8a261c6ffbaef27060d804d924e1259
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>