Change home directory permission to 0750

Currently the default home directory permission is set to 0755 and reinforced with DIR_MODE=0755 in /etc/adduser.conf. As we intend to make this a multi-user system to allow multiple user profiles such as "travel" "work" or "home" (or even "guest") in the form of users that you could switch between, backup and restore, we should modify /etc/adduser.conf so that DIR_MODE=0750 so that processes running as one user won't immediately be able to access files owned by another.