Changed IBNetService.GetBackground to take a hero instead of a class/gender combination
Added portraits getter in services
Trigger portraits download in MainViewModel to make it part of the "downloading career" screen
Feeding portraits downloaded in MainViewModel to CareerViewModel
Added heroes' portraits to tab items
Changed tab items text to something closer to Battle.net (eg. {level} {heroname})
Fixed Exocet font path (wasn't used anymore due to moving the HeroView to a subfolder)