changes analysis: add "deleted files" metrics in report

## Problem being solved
It's good to see if someone is getting rid of duplicated or unnecessary files in repo. Deleted lines in common files are considered a "change", "refactor", "churn", because it's in the context of a file that is being evolved.
We didn't want to mix those changes with the deletion of files, because it's not really a "change in 300 lines" when you are simply deleting a file, but the information about code shrinking due to make the codebase more sane is important too.

## Proposal
Add an additional metrics called "files removed/lines reduced" in the perspectives to show when this situation is happening.