added warning about number of destinations in msg composer and in IdDialog

retroshare-gui/src/gui/Identity/IdDialog.cpp

@@ -2387,6 +2387,10 @@ void IdDialog::sendMsg()
     if(selected_items.empty())
 	    return ;
 
+    if(selected_items.size() > 20)
+        if(QMessageBox::warning(nullptr,tr("Too many identities"),tr("<p>It is not recommended to send a message to more than 20 persons at once. Large scale diffusion of data (including friend invitations) are much more efficiently handled by forums. Click ok to proceed anyway.</p>"),QMessageBox::Ok|QMessageBox::Cancel,QMessageBox::Cancel)==QMessageBox::Cancel)
+            return;
+
     MessageComposer *nMsgDialog = MessageComposer::newMsg();
     if (nMsgDialog == NULL)
 	    return;

retroshare-gui/src/gui/msgs/MessageComposer.cpp

@@ -134,6 +134,7 @@ MessageComposer::MessageComposer(QWidget *parent, Qt::WindowFlags flags)
     m_completer = NULL;
     
     ui.distantFrame->hide();
+    ui.sizeLimitFrame->hide();
     ui.respond_to_CB->hide();
     ui.fromLabel->hide();
 
@@ -395,6 +396,11 @@ void MessageComposer::updateCells(int,int)
         ui.distantFrame->hide() ;
         ui.fromLabel->hide();
     }
+
+    if(rowCount > 20)
+        ui.sizeLimitFrame->show();
+    else
+        ui.sizeLimitFrame->hide();
 }
 
 void MessageComposer::processSettings(bool bLoad)
@@ -2770,7 +2776,10 @@ void MessageComposer::showTagLabels()
 		ui.tagLayout->addStretch();
 	}
 }
-
+void MessageComposer::on_closeSizeLimitFrameButton_clicked()
+{
+    ui.sizeLimitFrame->setVisible(false);
+}
 void MessageComposer::on_closeInfoFrameButton_clicked()
 {
 	ui.distantFrame->setVisible(false);

retroshare-gui/src/gui/msgs/MessageComposer.h

@@ -164,7 +164,8 @@ private slots:
     void tagRemoveAll();
     
     void on_closeInfoFrameButton_clicked();
-    
+    void on_closeSizeLimitFrameButton_clicked();
+
     static QString inviteMessage();
 
 private: