Create new account plugin

[zASSAz]

It will be fine to have new user registration plugin in chat. Something like "Register" button on login form.

[benlangfeld]

This shares goals and implementation details with #94

[ghost]

I think this would be a good plugin to have. For help & tips, converse.js has code for registering an account.

[singpolyma]

I have a basic plugin implementing this working locally

[gibus]

@singpolyma hello, I'm currently facing the same need and I'd be interested by your implementation (in order to not rewrite the wheel). It would be very kind if you can post it. Thx!

[gibus]

I think this issue can be closed with #167