Separate the global message data from the list display data

The messages being passed to the handlebars templates were global
messages which we were adding per list details to, show name bar etc.
This causes rendering bugs when you try to rerender a message, because a
different list may have changed it. This commit moves the global message
data to a msg attribute on the message_container which will contain the
per list attributes.

(imported from commit 26b1f0d2c72d6288a6d3e7ed5f8692426f2a97ad)

zerver/tests/frontend/node/templates.js

@@ -238,6 +238,7 @@ function render(template_name, args) {
 
 (function single_message() {
     var message =  {
+        msg: {
             include_recipient: true,
             display_recipient: 'devel',
             subject: 'testing',
@@ -245,6 +246,7 @@ function render(template_name, args) {
             content: 'This is message one.',
             last_edit_timestr: '11:00',
             starred: true
+        }
     };
 
     var html = render('single_message', message);