PlatformSettings: Separate platform-specific implementation
PlatformSettings: Introduce new font faces

osx/PlatformSettings: Add "TimesNewRoman" font face.
osx/PlatformSettings: Add "Courier" font face.
osx/PlatformSettings: Add "Helvetica" font face.
osx/PlatformSettings: Add "HelveticaNeue" font face.

windows/PlatformSettings: Rename CourierNew font face to Courier.