[Core][Control] Re-design control deletion

[gdt050579]

Control deletion / removal has to be redisign. Things to include:

• Closing somehting from the framework (a regular window) should dealocate the control
• Closing a modal window, should not dealocate the control (most likely that window was built on the stack and will self detele)
• For windows built on the stack, make sure the desrtuctor also deletes child controls
• Make sure that window manager can not delete a modal window
• Rethink a new way of keep references to controls via ControlReference<T> : Reference<Control>