src: clazy compiler warnings

get rid of most clazy warnings (https://github.com/KDE/clazy)
* range loop use refs
* qcolor ctor with ints
* missing Q_OBJECT macro
* use .constfirst instead of .first

enabled ccache for unix systems for fasterr recompiling
* if ccache is in path we use it now

src/lib_gui/qt/window/QtSplashScreen.cpp

@@ -95,3 +95,4 @@ void QtSplashScreen::drawContents(QPainter *painter)
 
 	painter->drawText(r, Qt::AlignLeft, m_string);
 }
+