Added /transcribe requested in issue #35

[HeySreelal]

To specifically transcribe voice messages - especially useful on group chats 🚀

• Added /transcribe command to specifically ask to transcribe reply_to_message
• Made the bot do not respond to voice messages in a group chat by default.

Reference: Issue https://github.com/backmeupplz/voicy/issues/35

[HeySreelal]

Sorry for closing this, for now, it was quite a tough time for me. I'll re-open the pull request once I'm back on track.