CLC-3987 Guard against nil attendee collections
Merge pull request #2707 from ctweney/clc-3987

CLC-3987 Guard against nil attendee collections
CLC-3965 - Added Ruby-Net-LDAP to Gemfile
CLC-3965 - Added LDAP connection settings
CLC-3965 - Working on LDAP functions for Canvas
CLC-3965 - Added Canvas::Synchronization model, seeded canvas_synchronization table to store last guest user sync timestamp
CLC-3965 - Added testext spec for LDAP connectivity