Add subscriber should be extended to allow adding guests

[pauljanes]

J is creating accounts on behalf of other users so that she can add them as subscribers to her classes when they are coming for the first time i.e. as a guest.

We should extend the add subscriber function to allow her to add a guest by specifying guest name and guest email without making the guest have a jasify account. The reason she does this is so that when they come to her class she can remember their name for better customer service. But as the first class is free and they may never come again it doesnt make sense to force these guests to create an account when all Jayne wants is to remember their name. And creating accounts on behalf of other people is for sure wrong and should be prevented (I raised a separate issue for this).