docs/config-rulebase-common: Fix links and update property docs

* Add documentation for the escapedSubject property (change events).
* Update list of valid statuses for a change: null is reported as an
  empty string and SUBMITTED doesn't seem to exist in Change.Status.
* Correct the name for createdOn patch set property.

Change-Id: Ie07b08634ef1973f15bb9a52bce935878c0d9c43