Do not copy private appointments

Case 1: Private appointment copied to shared store

1. Login with user2
2. Give secretary to user1
3. Login with user1
4. Create a private appointment
5. Open the shared calendar of user2
6. Copy the private appointment from user1's calendar to user2

Result: Appointment is copied, but not selectable/readable for user1 anymore
Note: When you log in with user2, private calendar item is visible and readable

Case 2: Private appointment copied to public store

1. Login with user1
2. Create a private appointment
3. Create a public calendar
4. Copy the private appointment to this public calendar
   Observe appointment is still marked as private
5. Login with user3
6. Open the public calendar
7. Open the private appointment

Result: Private appointment is readable and selectable

Expected:

When copying or moving a private item to any other store (public, shared):
1) Unset is as private
2) Show a pop-up:

Move action:

Title: Private item 
Msg: Moving this appointment will unset it as private. Are you sure you want to continue?
Action button: Continue
Grey button: Cancel

Copy action:

Title: Private item 
Msg: Copying this appointment will unset it as private. Are you sure you want to continue?
Action button: Continue
Grey button: Cancel

3) Disable private icon button when item will be created in public or shared.
4) Unset private toggle when item is marked as private first, then 'create in ' is switched to public, shared