client: lists headers: use padding instead of margin

No visual changes but allows to set a background color to the list header.

client/components/lists/list.styl

@@ -45,7 +45,7 @@
 
 .list-header
   flex: 0 0 auto
-  margin: 20px 12px 4px
+  padding: 20px 12px 4px
   position: relative
   min-height: 20px
 
@@ -73,10 +73,10 @@
 
   .list-header-menu
     position: absolute
-    padding: 7px
+    padding: 27px 19px
     margin-top: 1px
-    top: -@padding
-    right: -@padding
+    top: -7px
+    right: -7px
 
   .list-header-plus-icon
     color: #a6a6a6