feature: add proper infinite scroll

[vnglst]

Add infinite scroll, goal:

• reduce initial payload (e.g. load only first couple of kb of messages)
• add pagination to scroll through entire message history

Using RAD

• based on: https://gun.eco/docs/RAD
• storing messages becomes:

gun
  .get('user')
  .get('topic')
  .get('timestamp') 
  .put('hi there!')

• and retrieving them:

gun
  .get('users')
  .map()
  .get('topic')
  .get({ ".": { "*": "2020-05-10" }, "%": 10000 // only 10 kb of messages on 10th of May
  .map()
  .on((msg, msgId) => {
    // or maybe use once here to avoid too many listeners? 🤔 
    // store in state
   })