adds loadPixels back in re: #1588
adds loadPixels back in re: #1588

@hobzcalvin tagging you in case you want to take a look as this reverts part of  8952a7c6869ebeeb385ce5e97adf8efb6fc26dc0
dhowe/p5.js,johnpasquarello/p5.js,nucliweb/p5.js,bomoko/p5.js,black-kite/p5.js,sakshamsaxena/p5.js,kennethdmiller3/p5.js,processing/p5.js,kadamwhite/p5.js,mlarghydracept/p5.js,johnpasquarello/p5.js,sakshamsaxena/p5.js,bomoko/p5.js,processing/p5.js,karenpeng/p5.js,karenpeng/p5.js,kennethdmiller3/p5.js,Jared-Sprague/p5.js,mlarghydracept/p5.js,Jared-Sprague/p5.js,nucliweb/p5.js,joecridge/p5.js,limzykenneth/p5.js,dhowe/p5.js,black-kite/p5.js,kadamwhite/p5.js,limzykenneth/p5.js,joecridge/p5.js