share conection refactoring

[atarkowska]

Due to the new changes handled by decorator there is a need to rewrite share activation.
Right now there is no way to create new omero session without knowing user password. I also couldn't join share to use it as an omero session.

 File "/Users/ola/Dev/omero/components/tools/OmeroWeb/omeroweb/../omeroweb/decorators.py", line 68, in get_share_connection
    sf = cl.joinSession(sh.uuid)
 File "/Users/ola/Dev/omero/dist/lib/python/omero/clients.py", line 409, in joinSession
   return self.createSession(session, session)
 File "/Users/ola/Dev/omero/dist/lib/python/omero/clients.py", line 463, in createSession
   prx = self.getRouter(self.__ic).createSession(username, password, ctx)
 File "/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/Glacier2_Router_ice.py", line 107, in createSession
   return _M_Glacier2.Router._op_createSession.invoke(self, ((userId, password), _ctx))
PermissionDeniedException: exception ::Glacier2::PermissionDeniedException
{
   reason = Password check failed for '9c9f9fc9-743f-43c6-aaac-a90c639c5259': [user=my_user_name, created=2012-02-23 09:39:26.216, closed=2012-02-23 09:50:07.155248]
}

We need to have a way either to access shared data as a member directly using existing omero session or to activate connection while joining omero session specified by share uuid.