Base Tier Validation - Waiting status

This module extends the tier validation approval system with an extra status called Waiting. When a tier review is created, it can start as Waiting instead of Pending, which is useful when approvals must happen in a fixed order.

• On the tier definition form, a new checkbox "Notify Reviewers on reaching Pending" lets you decide whether reviewers should receive an email when their review becomes active.
• Reviews in Waiting status automatically move to Pending when appropriate: if the definition requires sequential approval, only the next review in the sequence moves forward; otherwise all waiting reviews move to Pending at once.
• When a review moves to Pending and the notification option is set, the possible reviewers are subscribed to the record and a message is posted to notify them.
• The overall validation status of a record now shows Waiting when at least one review is still waiting, instead of simply showing that validation is not done.
• Users who are allowed to bypass the sequence can approve a review directly from the Waiting state, and the usual accepted-review notification is sent.

The module touches the tier definition, tier review and tier validation models, and adds a field to the tier definition form. It also adjusts the review table display so waiting reviews are shown without a special status style.