Person.canWrite(), Person.canAccess() should not only work for the current user

For two reasons, a user can call the methods Person.canWrite() and Person.canAccess() only for himself:

1. These methods use the functions canWrite(), canAccess() from zope.security.checker, and these functions check the permissions of the user of the current interaction.
2. Calling these methods for other persons than the current user might leak sensitve information. We should probably allow these methods only for LP admins, or perhaps for teams where the current user is a member.