Jhbate/invite by key

@kentquirk could you take a look please. I still need to do a call,with a server token, to get the inviter user profile but that means a change to go-common 
How would you suggest we do it? How do other people do it? For example, in Dropbox or Google I can create a "shared link", that has a long unique string in the URL, that I can give to other people and anyone with the link can access that particular file or folder?