Pick a different shortcut for toggling the OSM layer

[bhousel]

Ok. I'm having a bad day already, but this just made my day worse. 😠 I accidentally did Cmd+W instead of Option+W and it just closed the tab.

Option+W is a terrible choice for a keyboard shortcut in a web application.
I feel actually bad that this has slipped my notice until now, anyway we have to change it to something else.