Add missing view states for all the App pages

[grojasv]

Adding any missing view states to improve the UX would be nice. The current status is:

CharacterOverviewPage

• Empty state
• Loading state
• Success state
• Failure state

CharacterDetailsPage

• Empty state
• Loading state
• Success state
• Failure state

FavoritesPage

• Empty state
• Loading state
• Success state
• Failure state