Comment/Thread editing: Only edit when there is an update (see issue #58)

This addresses the issue of Merboco polluting the merge request "last updated" data. Where Merbocop used to always update it's own comments and threads, it will now check that the new comment is different from the previous one before editing and do nothing if they are the same.

Additionally this adds a --dry-run option to full-inspection and improves reporting of comment behavior.