Upscale pixmap sequence images

Previously when loading a pixmap sequence you had to specify the exact size that will be looked up in the icon theme files and there was no way to upscale SVGs without them being very pixelated/blurry. This change addresses both problems by choosing the apropriate icon size to look up in the files depending on what the size parameter is and rendering the pixmap that contains all animation frames at a size that fits the one you chose (approach works with both raster and vector images). All tests for KIconThemes and KWidgetsAddons still pass.

Before	After