Refactor

[arifaydogmus]

• Bottender upgraded.
• Slash command support added. ( This requires to add slash commands (balance, deposit, withdraw) to bot on Slack console)

Refactoring

• sendDoge fn created to unify sending actions.
• command removed and simplified in src/index
• errors send to user as a ephemeral message. (visible only to user)
• Bot reacts to original channel message with cool doge gif after successful transaction
• Sends DM to user whom received some doge
• Multiple recipients support added to tip