Add Forget Principals to Get Tickets dialog

Add Forget Principals to Get Tickets dialog

And remove remnants of it from the "more" panel.

Clear the registry key that stores the principal list.
Also clear the autocomplete strings on the active control.

[kaduk@mit.edu: squashed commits and rewrote commit message.]

ticket: 7269 (new)
subject: forget principals functionality
queue: kfw
target_version: 1.10.4
tags: pullup