Clicky: map .name() to username

The *only* way to label your users with a meaningful name in Clicky is to pass a "username" property in their `clicky_custom.visitor` / `clicky_custom.session`  (same thing) object:

![](https://cldup.com/u9h_9Bo1-L.png)

this was brought to our attention by a user, [ticket here](https://segment.zendesk.com/agent/tickets/20280) and I think it makes sense for within clicky to map `identify.name()` to username so that users can make the most of the tool without having to pass a redundant 'username' trait to their other tools.

@amillet @harrietgrace @ndhoule 

lmk what you think! also, if there's a better way w/ js to trim the `name` values than `delete` i'm open to some code review haha.