Summary:
- use a wrapper class which simplifies the use of QPointer
  for the creation of local QDialogs
- some false positives are marked
- some dialogs not identified by krazy have the main window
  as parent, they may still cause a crash, when the program is killed

Test Plan:
Before:
- open "About KDevelop Platform" dialog
- "killall kdevelop" -> kdevelop closes (as intended), but with crash
After:
- open same dialog
- "killall kdevelop" -> kdevelop silently quits

Reviewers: #kdevelop, apol

Reviewed By: #kdevelop, apol

Subscribers: apol, anthonyfieroni, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6308