BUG: Update CTK to fix issue with ctkMenuComboBox

$ git lg 19c9668..68a1ce2 --no-merges

• a2cce54 - ctkXnatResource download function implemented (11 days ago) <Tom Doel>
• 6ab9b11 - BUG: Fixed missing list elements problem (25 hours ago) <Andras Lasso>
• d3af228 - Replaced Qt5::Gui dependency with Qt5::Widgets. (4 days ago) <Stefan Kislinskiy>
• b9393da - Set QT_INSTALLED_LIBRARY_DIR in case of Qt5. (7 days ago) <Stefan Kislinskiy>
• 055c319 - Change sleep duration from 200ms to 250ms. (11 days ago) <Stefan Kislinskiy>
• 30d745a - Add NOMINMAX definition to global compile flags. (11 days ago) <Stefan Kislinskiy>
• 5002282 - Fixed incompatibilities between Windows.h and Qt 5 (NOMINMAX). (12 days ago) <Stefan Kislinskiy>
• a1f5a9e - Fixed Qt4/5 MOC issues regarding QIconEngineV2. (13 days ago) <Stefan Kislinskiy>
• 8f8208d - Add missing error log context parameter. (13 days ago) <Stefan Kislinskiy>
• 4f9073e - ENH: Clear box icon replaced with a less harsh one, a simple 'x' that does not indicate error (3 weeks ago) <Csaba Pitner>
• c2b9c56 - Add ctkCollapsibleButton::flat property (3 weeks ago) <Julien Finet>
• 553ecd7 - Add documentation for ctk*PopupWidget (8 weeks ago) <Julien Finet>
• 8e9b0a0 - Added a Signal which is used to do something before the session is closed. (8 weeks ago) <Daniel Knorr>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23750 3bd1e089-480b-0410-8dfb-8563597acbee