[TIMOB-19824] Automatically call needsSave when user activity is updated

In TIMOB-19567 we concluded we can't support the official route for updating an user activity: 1. Listen to useractivitywillsave. 2. Set needsSave:true each time you have a change. 3. Update the user activity with the actual change when useractivitywillsave is fired. Instead you now have to: 1. Update the user activity each time you have a change. 2. Set needsSave:true each time you have a change. I'd request that we take care of step 2 for the users and set the property automatically when the users updates the user activity.