Make QQuickWebEngineProfile a publicly exported class.
This allows users to set up and manipulate the profile from
C++, and removes the ugly hack needed to access the cookie store.

Change-Id: I99e1a8c2cb99d9d1a14e1c78bec5948ba1282fb3
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>