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/core/test.ts

@@ -1,45 +1 @@
-screen.clear()
-brick.print("PXT!", 10, 30, Draw.Quad)
 
-brick.drawRect(40, 40, 20, 10, Draw.Fill)
-brick.setStatusLight(StatusLight.Orange)
-
-brick.heart.doubled().draw(100, 50, Draw.Double | Draw.Transparent)
-
-brick.buttonEnter.onEvent(ButtonEvent.Bumped, () => {
-    screen.clear()
-})
-
-brick.buttonLeft.onEvent(ButtonEvent.Bumped, () => {
-    brick.drawRect(10, 70, 20, 10, Draw.Fill)
-    brick.setStatusLight(StatusLight.Red)
-    brick.setFont(brick.microbitFont())
-})
-
-brick.buttonRight.onEvent(ButtonEvent.Bumped, () => {
-    brick.print("Right!", 10, 60)
-})
-
-brick.buttonDown.onEvent(ButtonEvent.Bumped, () => {
-    brick.print("Down! ", 10, 60)
-})
-
-brick.buttonUp.onEvent(ButtonEvent.Bumped, () => {
-    brick.print("Up!  ", 10, 60)
-})
-
-
-let num = 0
-
-forever(() => {
-    serial.writeDmesg()
-    pause(100)
-})
-
-/*
-forever(() => {
-    let v = input.color.getColor()
-    screen.print(10, 60, v + "   ")
-    pause(200)
-})
-*/