Merge 3.9 RC5 fixes into master (#6459)

* UI fixes for 3.9 (#6400)

* UI fixes for header icon alignment

* PLT-6569 - Fixing pin icon in header

* PLT-6505 - Updating z-index for emoji picker

* Updating z-index for overlaying sidebar

* PLT-6134 - Fix for emoji picker on comments

* Reverting emoji picker fix

* Fixing alignment for header icons

* Removing channel title changes

* Don't show mention badge for active channel (#6411)

* PLT-6583 - Fixing RHS compact view (#6413)

webapp/sass/layout/_headers.scss

@@ -7,7 +7,7 @@
     line-height: 56px;
     position: relative;
     width: 100%;
-    z-index: 5;
+    z-index: 9;
 
     .member-popover__trigger,
     .pinned-posts-button {

webapp/sass/layout/_navigation.scss

@@ -41,14 +41,6 @@
             width: 43px;
             z-index: 5;
 
-            > span {
-                > svg {
-                    position: relative;
-                    top: 13px;
-                    vertical-align: top;
-                }
-            }
-
             .icon-bar {
                 background: $white;
                 width: 21px;
@@ -57,8 +49,7 @@
             .icon-search {
                 font-size: 17px;
                 position: relative;
-                top: 11px;
-                vertical-align: top;
+                top: -2px;
             }
 
             .icon--white {

webapp/sass/layout/_post-right.scss

@@ -39,10 +39,6 @@
             }
         }
 
-        .post__img {
-            width: 43px;
-        }
-
         .post__body {
             width: 100%;
         }

webapp/sass/layout/_sidebar-right.scss

@@ -48,10 +48,6 @@
             }
         }
 
-        .post__img {
-            width: 43px;
-        }
-
         .post__content {
             padding: 0 10px 0 0;
         }