Swap X/y in images (#528)

* Swap X/Y in image encoding

* Fix PNG decoder

* Now really fix png

* reducing deps

* moving png.cpp into ev3

* bumped pxt

* updated shims

* fixing c++ compilation

* updated shims

* Fix pixel order

* update pxt

* Fix C++ image decoding

* Add expanded PNG images

* Generate E1 format images (in libs/ev3 run 'pxt buildsprites images')

* Go back to white background

* Remove PNG support

libs/screen/shims.d.ts

@@ -20,6 +20,13 @@ declare interface Image {
     //% property shim=ImageMethods::isMono
     isMono: boolean;
 
+    /**
+     * Sets all pixels in the current image from the other image, which has to be of the same size and
+     * bpp.
+     */
+    //% shim=ImageMethods::copyFrom
+    copyFrom(from: Image): void;
+
     /**
      * Set pixel color
      */
@@ -56,6 +63,12 @@ declare interface Image {
     //% shim=ImageMethods::flipY
     flipY(): void;
 
+    /**
+     * Returns a transposed image (with X/Y swapped)
+     */
+    //% shim=ImageMethods::transposed
+    transposed(): Image;
+
     /**
      * Every pixel in image is moved by (dx,dy)
      */