Handle alpha channel in colorize to support premultiplied

Change-Id: I660b4a66d878e2f02d442f9a77ddb35c0d51d5d2
Normalize quality parameter in the range 0..100 for all image formats

Change-Id: I52aac4b740e642b4241433201c46b83e2d4537f1
Handle rescaling parameters in WebP decoder

Handle maxWidth, maxHeight and scaleMode parameters in WebP decoder in
a consistent way with JPEG decoder.

Change-Id: I372c69d7107161d71f5037321a37bbbbcaac6322