PLT-5747: Fixed inconsistent on-hover, tooltip, and active states for buttons. (#7174)

* Fixed LHS Team Sidebar on hover highlight.
 * Fixed LHS Main Menu on hover tooltip to show "Main menu".
 * Added On-hover highlight for Favorite button in channel heading.
 * Added active state for channel members icon.
   * Added active class based on internal react state with new changeCss rule.
 * Changed cursor to pointer on hovering a theme.
 * Fixed Invite New Member Add Button to have text-underline on hover.

webapp/sass/components/_modal.scss

@@ -692,3 +692,9 @@
         padding-left: 0;
     }
 }
+
+.modal-invite-member {
+  .btn:hover {
+    text-decoration: underline;
+  }
+}