Add url option to autostart walkthrough

[bhousel]

suggested here: #3921 (comment)

It might be useful to provide a url option to put the user directly into the walkthrough.

[althio]

I tried http://preview.ideditor.com/master/#walkthrough=true and it works 🙇
What will be the url on production http://www.openstreetmap.org/edit?editor=id once deployed?

[bhousel]

What will be the url on production http://www.openstreetmap.org/edit?editor=id once deployed?

It will be similar, just add a walkthrough=true param to the hash part of the url, so something like http://www.openstreetmap.org/edit?editor=id#walkthrough=true