follow up for IDEA-122272
(cherry picked from commit 390cc17) [r=Peter.Gromov]
IDEA-122125 "Close Active Task" fail on commit

(cherry picked from commit 75dea1d247fa4ba9f548f1392d435b5a632ce2f4)
Cleanup (dead code, typos)
ui: allow borderless popups
ui: about dialog converted to popup