Added support for secrets file & Active Directory authentication

[PeteDiMarco]

Hi-
I've made several changes & additions to ISLE. I recommend reviewing the diffs carefully before accepting them. This was my first project in PHP.

Documentation:
devel-notes.txt : Database schema
isle-rest-api.txt : REST API

Utilities:
isle-init.py : Smarter version of isle-init.sh. Uses Secrets.php.

Source Files:

• webroot/isle/users.php : Added hooks to ActiveDirectory.php. Needs clean-up.
• webroot/isle/includes/auth.php : Added hooks to Secrets.php. Definitely could be cleaner.
• webroot/isle/includes/classes/ActiveDirectory.php : Authentication through Active Directory. Should be adaptable to other LDAPs. Needs comments.
• webroot/isle/includes/classes/AuthMode.php : Simple enumeration of ways to connect to Active Directory.
• webroot/isle/includes/classes/Secrets.php.template : This is the template file for Secrets.php. Stores site-specific info for LDAP/Active Directory, database connection, time zone, and Admin password.