Update to 3.6.0.

Announcement:
http://blog.qt.io/blog/2015/12/15/qt-creator-3-6-0-released/

Changes:
http://code.qt.io/cgit/qt-creator/qt-creator.git/tree/dist/changes-3.6.0.md?h=3.6

Submitted by: Ralf Nolden <nolden@kde.org>