Apply translations on input type submit

Commit 3729976 only updated xgettext.html which generates the .pot file.
This commit also makes sure that the actual translations are applied to
the interface.

Fixes #997

app/localization.js

@@ -147,7 +147,7 @@ Localizer.prototype = {
                 }
                 if (elem.hasAttribute("value") &&
                     elem.tagName === "INPUT" &&
-                    isAnyOf(elem.getAttribute("type"), ["reset", "button"])) {
+                    isAnyOf(elem.getAttribute("type"), ["reset", "button", "submit"])) {
                     translateAttribute(elem, "value");
                 }
             }