added ofPixels::setColor(ofColor) and ofImage::setColor(ofColor). closes #1910.
Merge branch 'develop' of github.com:openframeworks/openFrameworks into feature/setColor-fill
added made color const for setColor, added setColor for index, made setColorfor the entire image faster per suggestion from @arturoc
Merge pull request #1912 from kylemcdonald/feature/setColor-fill

added ofPixels::setColor(ofColor) and ofImage::setColor(ofColor)