MDL-1626 mod_forum: Only drop discussion preferences when the subscription change was initiated by the user
MDL-1626 mod_forum: Make cron handle discussion subscriptions
MDL-1626 mod_forum: Initial notification tests
MDL-1626 mod_forum: Add functions to unsubscribe a user from a discussion
MDL-1626 mod_forum: Basic tests for per-discussion subscription
MDL-1626 mod_forum: Change to per-discussion subscription option in new post form
MDL-1626 mod_forum: Add a function to determine if the user is subscribed to a discussion
MDL-1626 mod_forum: Per-discussion subscription toggling

Still needs JS implementation.
MDL-1626 mod_forum: Add unit tests for forum subscription changes