[REF] web, mail: minors UI fixes

- List view: sortable icon, do not force position to right
- Mail: do not vertically reposition systray's icons
- Form view: oe_subtotal_footer, minor design imp

addons/mail/static/src/less/systray.less

@@ -3,7 +3,6 @@
     > a {
         opacity: 1;
         > i {
-            .o-transform(translateY(4px));
             font-size: larger;
         }
     }

addons/web/static/src/less/form_view.less

@@ -461,10 +461,14 @@
             }
         }
 
+        > tbody > tr:first-child > td {
+            padding-top: 4px;
+        }
+
         .oe_subtotal_footer_separator {
             width: 100%;
             text-align: right;
-            border-top: 1px solid @odoo-brand-secondary;
+            border-top: 1px solid @gray-lighter-dark;
             font-weight: bold;
             font-size: 1.3em;
         }

addons/web/static/src/less/list_view.less

@@ -37,7 +37,8 @@
         .user-select(none);  // Prevent unwanted selection while sorting
 
         &::after {
-            .o-position-absolute(@right: 3px);
+            margin-left: 6px;
+            position: absolute;
             font-family: FontAwesome;
             content: "\f0d7";
             opacity: 0;