[FIX] im_livechat: livechat button not rely on JS services

Revision of https://github.com/odoo/odoo/commit/02ec09cb1c3e2d7bc7968f40c18f2208d7f3f498

One of the purposes of the previous commit was to test discuss.
There was an attempt to test im_livechat, but it has been aborted due to the possibility
to use livechat on an external website.

However, some bits remain from this attempt, such as LivechatButton becoming a JS service
provider in order to use those services with the external lib. LivechatButton was not working
for the following reasons:

    - ServiceProviderMixin.init was not called (so it couldn't load any service);
    - On website, there are two service providers (LivechatButton & websiteRootInstance).

This fix ensures that LivechatButton does not rely on JS services, such as the bus_service.

addons/im_livechat/static/src/js/im_livechat.js

@@ -1,9 +1,9 @@
 odoo.define('im_livechat.im_livechat', function (require) {
 "use strict";
 
+var bus = require('bus.bus').bus;
 var config = require('web.config');
 var core = require('web.core');
-var ServiceProviderMixin = require('web.ServiceProviderMixin');
 var session = require('web.session');
 var time = require('web.time');
 var utils = require('web.utils');
@@ -33,11 +33,7 @@ if (!_.contains(url_history, page)) {
     utils.set_cookie(LIVECHAT_COOKIE_HISTORY, JSON.stringify(url_history), 60*60*24); // 1 day cookie
 }
 
-/**
- * In order to handle services like ajax in the external lib,
- * The parent of Livechat, LivechatButton, is set as a service provider
- */
-var LivechatButton = Widget.extend(ServiceProviderMixin, {
+var LivechatButton = Widget.extend({
     className:"openerp o_livechat_button hidden-print",
 
     events: {
@@ -56,7 +52,7 @@ var LivechatButton = Widget.extend(ServiceProviderMixin, {
         this.chat_window = null;
         this.messages = [];
         this.server_url = server_url;
-        this.busBus = this.call('bus_service', 'getBus');
+        this.busBus = bus;
     },
 
     willStart: function () {

addons/im_livechat/views/im_livechat_channel_templates.xml

@@ -142,7 +142,6 @@
             <script type="text/javascript" src="/web/static/src/js/services/local_storage_service.js"></script>
             <!-- Bus, Mail, Livechat -->
             <script type="text/javascript" src="/bus/static/src/js/bus.js"></script>
-            <script type="text/javascript" src="/bus/static/src/js/services/bus_service.js"></script>
             <script type="text/javascript" src="/mail/static/src/js/chat_window.js"></script>
             <script type="text/javascript" src="/mail/static/src/js/thread.js"></script>
             <script type="text/javascript" src="/mail/static/src/js/document_viewer.js"></script>

addons/website_livechat/views/website_livechat.xml

@@ -9,7 +9,6 @@
         <template id="assets_frontend" name="im_livechat assets frontend" inherit_id="website.assets_frontend">
             <xpath expr="." position="inside">
                 <script type="text/javascript" src="/bus/static/src/js/bus.js"></script>
-                <script type="text/javascript" src="/bus/static/src/js/services/bus_service.js"></script>
                 <script type="text/javascript" src="/mail/static/src/js/chat_window.js"></script>
                 <script type="text/javascript" src="/mail/static/src/js/document_viewer.js"></script>
                 <script type="text/javascript" src="/mail/static/src/js/thread.js"></script>