Restrict selecting characters that are already initialized

[landalex]

[jleung51]

For clarification: upon selecting a character which has already been selected, the server responds with HTTP 409: Conflict. The app should prevent the player from selecting this character.

The app can also display player selection state during the selection screen through this API.

[jleung51]

Reclassified as a bug because this is unintended behaviour, and the feature addition is simply unimplemented.