Raise minimum Qt version

Needed for supporting more C++11 features.

Change-Id: Ib3ab63b2698c86a1ad0153c3e4bead09cccdefca
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

qtcreator.pro

 include(qtcreator.pri)
 
 #version check qt
-!minQtVersion(5, 3, 1) {
+!minQtVersion(5, 4, 0) {
     message("Cannot build Qt Creator with Qt version $${QT_VERSION}.")
-    error("Use at least Qt 5.3.1.")
+    error("Use at least Qt 5.4.0.")
 }
 
 include(doc/doc.pri)