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/sass/layout/_post.scss

@@ -236,6 +236,26 @@
         display: none;
     }
 
+    .post-list__loading {
+        @include opacity(.5);
+        font-size: .9em;
+        font-style: italic;
+        padding: 1em 0;
+        text-align: center;
+
+        i {
+            margin-right: 2px;
+        }
+
+        &.post-list__loading-search {
+            cursor: pointer;
+
+            &:hover {
+                text-decoration: underline;
+            }
+        }
+    }
+
     .post-list-holder-by-time {
         -webkit-overflow-scrolling: touch;
         background: #ffffff;