MakeCode GitHub integration

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I hope it's okay to Copy and Paste your feedback @martinwork. I think it's relevant to add as an overall issue to improve the experience of using GitHub within the app.

After signing in to save a project to GitHub, once back in MakeCode, the back button on the device leaves the user at the Github website 404 page.

More.../Sign out of GitHub leaves the user at the Github website home page. Two presses of the back button return to MakeCode. In the iOS app, I added a trap to recognise this and boot back to MakeCode, with a back button showing in case that didn't work.

Once signed out, the GitHub tick button is still showing. Tapping it leads to a message saying "Go to Github", which 404s.
The Github attachment is not remembered for the next run.

These last two points are the same in the iOS app, though I believe it used to work, so I think this is a MakeCode change/regression.

I think any time you need to sign in to Github, MakeCode should show the sign in dialogue, not a link to the website.