Warning dialog on empty new item

Created by: Theonimfi

Create warning_dlg.py base on safe_delete_dlg.py and modify rest_action_list_wt.py and breathing_phrase_list_wt.py. The aim is to inform the users what they have to do if they press the button 'Add' without adding a new item. The warning_dlg.pycreates the dialog. In rest_action_list_wt.py and breathing_phrase_list_wt.py I import the mc.gui.warning_dlg. In add_new_phrase_button_clicked method and in add_rest_action_clicked method i call the mc.gui.warning_dlg to connect with the dialog and to create the message that this dialog would have.