Fixups and enhancements

Summary

• Fix bug where you can evolve the same pokemon over and over. I feel like that might cause unintentional spam, so once you've seen the evolved pokemon, you can't evolve it again.
• Show the "chosen" pokemon when someone types the !list command. I figured it would be good since there's currently no other way to see the chosen pokemon except looking through the message history.
• Uptake the http health server from version 0.0.4 of go-common.
• Adjust the timezone to UTC instead of ET