Bugfix/run twice

[murilopolese]

Problem:

Person clicks on run twice for a code with a long execution or simple stop it and editor starts misbehaving.

Interrupt first execution but won't run the second time
Sometimes get stuck on raw repl
Sometimes run button stops working
This will also make other functions to break (save, list files, etc...)

Solution:

Update front end to use new feature from micropython.js to ensure a prompt.
Here's the micropython.js PR for reference.

[ubidefeo]

LGTM