*Title: Section Assign policy.

*Documentation:
The 'assign' function was added to the list of policy functions
for the module 'section'. This gives possibility to deny users from
assigning/reassigning objects to desired sections. The policy has
following limitations:

- Class	       - the class of the object which user trying assign the section to.
- Section      - the current section of the object.
- Owner	       - the owner of the object (Any or Self)
- NewSection   - the section which is allowed to be assigned by the user.