[IMP] pos restaurant: prevent an offline table removal from floor screen

- Current pos restaurant with offline mode, when you delete the table from
  floor screen, it would stop everything (you won't be able to create an order
  further) untill your server start again, that is not good indeed.
  Instead we should show the error popup, just like you will get when you click
  on '+' for adding a new table on offline mode.

- Slightly improve the other relevant warning messages.

- Only pos managers can edit the floor screen.
  Before this pos user were allowed to access the edit button (pencil
  icon on floor screen), but they could never update the table detail
  as lack of permission so in this we have prohibited the pos user
  from accessing an edit button(pencil icon).

addons/pos_restaurant/static/src/js/floors.js

@@ -258,7 +258,7 @@ var TableWidget = PosBaseWidget.extend({
         }, function(err,event) {
             self.gui.show_popup('error',{
                 'title':_t('Changes could not be saved'),
-                'body': _t('Check your internet connection and access rights'),
+                'body': _t('You must be connected to the internet to save your changes.'),
             });
             event.stopPropagation();
             event.preventDefault();
@@ -292,6 +292,13 @@ var TableWidget = PosBaseWidget.extend({
             }
             floorplan.update_toolbar();
             self.destroy();
+        }, function(err, event) {
+            self.gui.show_popup('error', {
+                'title':_t('Changes could not be saved'),
+                'body': _t('You must be connected to the internet to save your changes.'),
+            });
+            event.stopPropagation();
+            event.preventDefault();
         });
     },
     get_notifications: function(){  //FIXME : Make this faster
@@ -402,7 +409,7 @@ var FloorScreenWidget = screens.ScreenWidget.extend({
             .call('set_background_color',[this.floor.id, background]).fail(function(err,event){
                 self.gui.show_popup('error',{
                     'title':_t('Changes could not be saved'),
-                    'body': _t('Check your internet connection and access rights'),
+                    'body': _t('You must be connected to the internet to save your changes.'),
                 });
                 event.stopPropagation();
                 event.preventDefault();

addons/pos_restaurant/static/src/xml/floors.xml

@@ -107,7 +107,7 @@
                         This floor has no tables yet, use the <i class="fa fa-plus"></i> button in the editing toolbar to create new tables.
                     </div>
                     <div class='tables'></div>
-                    <span class='edit-button editing'><i class='fa fa-pencil'></i></span>
+                    <span t-if="widget.pos.user.role == 'manager'" class='edit-button editing'><i class='fa fa-pencil'></i></span>
                     <div class='edit-bar oe_hidden'>
                         <span class='edit-button new-table'>
                             <i class='fa fa-plus'></i>