Some improvements: error logs, stickers IDs and settings commands on startup

• Added error logs to file, so that you can easily track and squash those nasty bugs!
• If you send/forward bot a sticker, bot will tell you the ID of that sticker. Unlike other media files in Telegram, stickers' IDs are the same across different bots.
• Setup bot commands on startup (unfortunately, this will override all other commands, so feel free to open an issue about this).