[IMP] pad: Use standard full screen icon and add tooltips

replace the icon for fullscreen by the same one used on YouTube (or a similar one) + add tooltip 'Full Screen' and 'Exit Full Screen'

addons/pad/static/src/js/pad.js

@@ -23,7 +23,9 @@ var FieldPad = form_common.AbstractField.extend(form_common.ReinitializeWidgetMi
         var self = this;
         this.$('.oe_pad_switch').click(function() {
             self.$el.toggleClass('oe_pad_fullscreen');
-            self.$el.find('.oe_pad_switch').toggleClass('fa-expand fa-compress');
+            var pad_switch = self.$el.find('.oe_pad_switch').toggleClass('fa-arrows-alt fa-compress');
+            var title = pad_switch.hasClass('fa-compress') ? _t('Exit full screen') : _t('Full screen');
+            pad_switch.attr('title', title);
             self.view.$el.find('.oe_chatter').toggle();
             $('#oe_main_menu_navbar').toggle();
         });

addons/pad/static/src/xml/pad.xml

@@ -11,7 +11,7 @@
             </t>
             <t t-if="! widget.get('effective_readonly')">
                 <div class="oe_pad_switch_positioner oe_configured">
-                    <span class="fa fa-expand oe_pad_switch" />
+                    <span title="Full screen" class="fa fa-arrows-alt oe_pad_switch" />
                 </div>
                 <div class="oe_pad_content oe_editing oe_configured" />
             </t>