private void removeButton_Click(object sender, EventArgs e)
        {
            if (sourcesListBox.SelectedItem != null)
            {
                try
                {
                    client.RemoveSource((string)sourcesListBox.SelectedItem);
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }

                DisplaySources();
            }
        }