[FIX] web_editor, mass_mailing: better transcode alignment inheritance

Browsers' default alignement of <td/> is 'inherit'. Some mail clients do
not set this value properly though and even if it is explicitely set,
they do not compute the final value well.

As a fix, this commit forces the 'inherit' value on <td/> and computes
the real alignment for 'inherit' values when transcoding.

opw-813688

addons/mass_mailing/static/src/less/themes/theme_default.less

@@ -46,6 +46,11 @@
     background-color: @o_mm_def_color_alpha;
 }
 
+td {
+    // Default browser style but needed so that alignment works on some mail
+    // clients (see transcoder)
+    text-align: inherit;
+}
 
 // ===== Layout =====
 .o_layout {

addons/web_editor/static/src/js/transcoder.js

@@ -131,6 +131,20 @@ var getMatchedCSSRules = function (a) {
         delete style['text-decoration-style'];
     }
 
+    // text-align inheritance does not seem to get past <td> elements on some
+    // mail clients
+    if (style['text-align'] === 'inherit') {
+        var $el = $(a).parent();
+        do {
+            var align = $el.css('text-align');
+            if (_.indexOf(['left', 'right', 'center', 'justify'], align) >= 0) {
+                style['text-align'] = align;
+                break;
+            }
+            $el = $el.parent();
+        } while (!$el.is('html'));
+    }
+
     return style;
 };