win32: Improve GtkAssistant theming

The highlighted color chosen for GtkAssistant header font
(deep blue) makes it hardly readable is most cases. Switch
to light gray.
https://bugzilla.gnome.org/show_bug.cgi?id=696171
win32: Bring back spinner animation

Define the spinner animation in css.
https://bugzilla.gnome.org/show_bug.cgi?id=696202
win32: add more width to the slider to not cut it when using marks
win32: add margin to scale trough
win32: set color for scale marks
win32: scale slider with marks was off by 2 pixels
win32: handle again gtk-font-name

This code is ugly but it seems to do the work
3.6.5
Bump version