White screen if a logged out user click in aprove or reprove e-mail link

Move logged in check from "page callback" to "access callback" and check if can accept ou iginore trusts request to send a forbidden page

To reproduce the blank page response:

1. Send a trust request to other user
2. copy the trust link from email or /contacts page
3. disconect
4. acces the trust link in a logged out browser.