Move opt/aside.png to JSDuck wiki.

Hosting the file inside the wiki repository instead makes much more sense.
Switch @key and @pattern around in BooleanTag.

Let the @key be aut-created from @pattern instead - requirering each
BooleanTag implementation to define @pattern.

This will help with writing Custom Tags tutorial, where I can introduce
the @pattern field first.
Fix the initialization of #key field in @new tag.

Add a smoke test to ensure we'll catch such a thing in the future.