Allow sharing public links

[dsonck92]

As an artist, I don't want to require my clients to sign up to my cloud. Some clients are very conscious about their accounts and don't want the burden of maintaining (and trusting) yet another platforms login credentials. (yes, I've heard the complaint from someone already when migrating over Voltaserve, but he'll do more things in the future so I don't agree with him here 😉, it's much more convenient for the both of us to have an account)

I would like to be able to create a link which has the same kind of role selection as current sharing options:

• Editor: Sometimes I need my external artists to upload content to me
• Viewer: Sometimes I need to share my works to external parties