Qt Graphical Effects RHIification

Qt Graphical Effects is not usable on the QRhi-based rendering path of Qt Quick.

Out of the 25 effects 15 are trivial to port, 10 are based on dynamic shader strings. Out of the 10, 2 are essential (Glow, DropShadow). Those can be handled by limiting them to the "fast" rendering path which, in Qt 5.5 and earlier, was still based on a static shader code.

All in all this means that we can make 17 effects working with minimal effort, while the remaining 8, mostly the advanced, high quality (and less often used due to being a perf. hazard) blurs, should probably disappear.