Show correct error icons/messages

[pimvullers]

The difference between transaction errors and missing or invalid credentials is not clear. This depends on improved exceptions from the credentials API (credentials_api issue #5).

[pimvullers]

According to Jaap-Henk there are some things wrong that could be fixed without exception handling:
If the card has the right credential but not the right attribute, it says "attribute missing". However, if the complete credential is missing it says "Please try again". In this case it should say "Credential missing"