room-history: Increase padding of SenderAvatar

Makes the hover effect around the avatar bigger, which makes it more
obvious that it behaves like a button.

data/resources/stylesheet/_room_history.scss

@@ -102,7 +102,7 @@ room-title {
 }
 
 sender-avatar {
-  padding: 3px;
+  padding: 5px;
   border-radius: 100%;
 
   @include vendor.focus-ring();

src/session/view/content/room_history/message_row/mod.ui

@@ -6,7 +6,7 @@
         <style>
           <class name="event-content"/>
         </style>
-        <property name="column-spacing">12</property>
+        <property name="column-spacing">8</property>
         <child>
           <object class="ContentSenderAvatar" id="avatar">
             <layout>