PLT-6215 Major post list refactor (#6501)

* Major post list refactor

* Fix post and thread deletion

* Fix preferences not selecting correctly

* Fix military time displaying

* Fix UP key for editing posts

* Fix ESLint error

* Various fixes and updates per feedback

* Fix for permalink view

* Revert to old scrolling method and various fixes

* Add floating timestamp, new message indicator, scroll arrows

* Update post loading for focus mode and add visibility limit

* Fix pinning posts and a react warning

* Add loading UI updates from Asaad

* Fix refreshing loop

* Temporarily bump post visibility limit

* Update infinite scrolling

* Remove infinite scrolling

webapp/i18n/en.json

@@ -1887,6 +1887,7 @@
   "post_info.unpin": "Un-pin from channel",
   "post_message_view.edited": "(edited)",
   "posts_view.loadMore": "Load more messages",
+  "posts_view.loadingMore": "Loading more messages...",
   "posts_view.newMsg": "New Messages",
   "posts_view.newMsgBelow": "New {count, plural, one {message} other {messages}} below",
   "quick_switch_modal.channels": "Channels",