Auth changes

For your information: the changes I made to enable (basic and) ldap authentication.

Note: to use this, you need:  sudo apt-get install python-paste
(My notes do not mention a need for apt-get to get python ldap support; I am now unsure wether it really is not needed, or just an omission from my notes).

Note that I run this via stunnel, set-up via the ~/screenly/misc/enable_ssl.sh script provided with screenly.
Note that when you enable stunnel using that script, you have to change the firewall rules to open port 443, by issuing: sudo ufw allow 443/tcp
Probably this should be fixed in the ~/screenly/misc/enable_ssl.sh script.