restructure codebase in modules

[arantespp]

The codebase is growing and we need to create the modules to keep it organized. I think these modules make sense:

• [ ] Publish: manage publishing memes on social media—Twitter, Instagram, LinkedIn, Facebook, and so on.
• [ ] Transform: transform media—add the logo, add messages... to meme. It receives a buffer and returns a buffer. https://github.com/sibelius/ccsseraphini/issues/1457
• [ ] Receive: handle media input. Users can send memes from Discord, Twitter DM, the website, etc. This module receives the media and sends it to voting. https://github.com/sibelius/ccsseraphini/issues/1448
• [ ] Voting: receive the transformed media and send it to the Discord voting channel. If approved, it sends to Publish.
• [ ] TwitterMentions: handle Twitter mentions—show mentions on the Discord meme channel and provides a mechanism to retweet them.