Add timestamps for Reviewer/Admin

[ldang]

When the Reviewer or Admin comes in and tweaks the start/end time or the flags, it will update "Last edited by:" credit to the Reviewer display name. This will obscure who the original Editor was.

Could we have a "Last edited by:" and "Last reviewed by:" credit, so the editor credit isn't clobbered.

Reasons to retain editor info:

1. Nice to go back to original editor if there are questions
2. May want to provide notes to editor on how to provide better comments or kudos if very little needed to be done during review time.
3. Makes it more obvious who did the editing. Since I am the primary reviewer this year, every time I review a talk, it looks like I did all the editing, and nobody else contributed.