Fix foreign key issues

Add missing :dependent to all associations not to left orphan
records behind causing foreign key constraint issues

See https://trello.com/c/dXnTk6hd/222-resolve-issues-with-foreign-keys-and-deleting-objects

Fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=996685
https://bugzilla.redhat.com/show_bug.cgi?id=1013120
https://bugzilla.redhat.com/show_bug.cgi?id=1017140
https://bugzilla.redhat.com/show_bug.cgi?id=1002495
https://bugzilla.redhat.com/show_bug.cgi?id=988950
https://bugzilla.redhat.com/show_bug.cgi?id=1013837