pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/lessons/screen-wipe/activity.md

@@ -2,13 +2,13 @@
 
 Clear the screen by pressing buttons on the @boardname@ 
 
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 This activity will teach how to clear the screen by pressing button A on the @boardname@.
 
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 You can use the clear screen` function to turn off all the LED on the screen. Let's illustrate this concept with a small script where the user has to press the button A to turn off the screen. Let's start by adding the code to show an animation.
 
@@ -82,9 +82,9 @@ input.onButtonPressed(Button.A, () => {
 
 *Run* the script in the simulator or on the @boardname@ to see how this works!
 
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+## ~avatar boothing
 
 Excellent, you're ready to continue with the [challenges](/lessons/screen-wipe/challenges)!
 
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