Implement ResponseHandle class

[Piturnah]

The ResponseHandle should manage the prettier formatting (#1) and all guild_messages.

No more callbacks from the Game class to the Bot class, except when the Session actually ends.
This could be lazily, as in the Game just goes into a ENDED state and the Bot checks that and removes it on the next user interaction in the channel

[jreppnow]

Partially implemented via CommandParser class, which removed the need for callbacks to the Bot class. However, for better message, something like this might still be desirable.

[jreppnow]

I extracted all the messages into the Messages class, but this might still warrant further improvement, for which this ticket seems useful.