Ray-Tracing now handles IBL and background cubemaps in similar way as PBR.
Ambient light source is handled by Ray-Tracing in similar way as PBR,
e.g. as coefficient for environment map (IBL) or as constant light source.
Test script generating PBR spheres has been moved to Samples
and now shared by PBR and Path-Tracing tests.
ViewerTest::ParseColor() - fixed alpha component defined as 255 for RGB-only input.
Quantity_Color::ColorToHex() now rounds-up float values to closest integer.
Quantity_ColorRGBA::ColorToHex() - added method formatting color into hex with alpha component consistent to Quantity_Color::ColorToHex() for RGB.
vdrawtext command now uses ViewerTest::ParseColor() for parsing color argument, so that it accepts hex.
vreadpixel command now has been extended with -hex argument for printing color in hex format.
Commands XSetColor, XGetColor, XGetShapeColor, XGetAllColors, XAddColor, XRemoveColor, XFindColor,
XUnsetColor, XGetInstanceColor, XSetInstanceColor have been corrected to properly report syntax input errors
and to accept color names and hex (by reusing ViewerTest::ParseColor()).
