Adds support for 'italic' font-style when using @font-face fonts

@font-face fonts do not always offer italic versions, and if they do, they require the loading of separate font files.  This means that setting fontStyle to 'italic' rarely works when using non-system fonts.

This minor patch prevents the native use of fontStyle 'italic' and instead apply's a small transform to emulate the italic style for all fonts.

This could be further improved by checking whether the fontFamily is a non system font (by simply checking through an array of defined system fonts) and only using the transform method as a fallback when needed