Check possibility to inform user via client alert about WW mode deactivation

[ChristianeMussmacher]

As discussed in team meeting 16.01.2017:

• We are looking for a way to inform clients that have not yet updated to the latest update (w/o ww feature) that the feature is not available anymore
• Preferably, an alert is shown when user tries to start ww mode by opening ww tab
• In case it is not possible to show alert / toast, a push notification should be sent to client with according information