Track when task / issue is added or removed from an iteration

[#1]

It would be great if we could track when tasks and issues are added to or removed from an iteration.

Use cases:

1. Some tasks are added mid-sprint and it would be nice to know which were committed to in sprint planning and which were added later.

2. When tasks aren't completed in a sprint and they carry-over / move to the next sprint it would be nice to easily see and report off of that.

3. If something is moved out of a sprint to the backlog it would be nice to easily see and report off of that.

All of this would be helpful in seeing a team's velocity and knowing what their trends are. It's currently difficult to see the life of a task.

[#2]

Atleast an iteration "Lock" feature will aid in freezing the iteration (lock from iteration start date to iteration end date) with the original set of tasks and be able to report off of that.