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/responsive/_tablet.scss

@@ -105,7 +105,7 @@
                 right: -1px;
             }
 
-                    .send-button {
+            .send-button {
                 display: table-cell;
             }
         }
@@ -126,6 +126,7 @@
     .sidebar--right {
         @include single-transition(all, .35s, ease);
         @include translateX(100%);
+        z-index: 10;
 
         &.move--left,
         &.webrtc--show {