FIX NPE

git-svn-id: https://tdam-2013-g5.googlecode.com/svn/trunk@171 0117bdac-9510-e2bd-253c-24df4fda417d
Agrega modelo MensajeWeb

git-svn-id: https://tdam-2013-g5.googlecode.com/svn/trunk@172 0117bdac-9510-e2bd-253c-24df4fda417d
Guarda/usa timestamp del ultimo mensaje web recibido

git-svn-id: https://tdam-2013-g5.googlecode.com/svn/trunk@173 0117bdac-9510-e2bd-253c-24df4fda417d