Add accountless ticket verification scheme

[JoeGruffins]

Depends on #7

There is a pr open in dcrstakepool decred/dcrstakepool#514 That allows for verification of ownership of a ticket without any login credentials. This is difficult to test without a client. I think that TD is the perfect testing ground for these api changes. Again, hopefully everything will work great and both that code and the code written here will make it into master.

[buck54321]

If you don't mind, I'm going to assign you here and #16, @JoeGruffins. You can roll everything into #22, or break up the work as you see fit.

I think that TD is the perfect testing ground for these api changes

I agree.