Automatically clean up stale change requests

In order to avoid having a wiki polluted with many change requests staled, we should provide a mechanism to clean them up.
We probably need a scheduler running daily performing two task:

• notify when a change request is about to be closed
• automatically close change requests after a delay

There should be several configurations for this scheduler:

• what date to consider to use for the delay (creation date of the CR, or update date)
• how much time to consider before closing it
• how much time before closing to consider before sending a notification