CB-6684 [3.5.0rc][Windows8] Splash screen setting breaks the build

https://issues.apache.org/jira/browse/CB-6684
1. Copies image instead of changing reference - this is correct way since img could be outside the project so it won't work (also, Windows8 splash screen plugin requires default splash screen location)
2. Warns instead of build failure if splash screen reference is not a file 
3. Fixed mixed tabs and spaces, all actual changes are under  #Splash screen support