Marking variable as private should regen screens where it's set

[vchelaru]

1. Create Entity
2. Add variable to Entity called Health, make sure it's public
3. Add EntityInstance to screen
4. Set EntityInstance.Health to some value
5. Select Health in Entity and make it private instead of public
6. Compile game

Observe - compile error in Screen happens because the variable is still assigned
Observe 2 - variable still appears in the named object list
Expected - this variable should get removed. Tell the user this will happen and let them decide
Expected 2 - the variable should no longer appear in the list of variables.