Reduce Trade dependencies

[Sjors]

I need to get rid of some circular dependencies in Trade. That should also make writing tests easier.

• move .trades reference to delegate : avoids having to pass coinify.trades along to new Trade objects
• pass save() method directly, or use delegate
• remove trade._coinify

Also added more debug statements.

[Sjors]

@jtormey with this first commit, I'm seeing a cannot find refresh() of undefined method when a payment is received, though everything seems to work. Can you try that on your end?

[jtormey]

You don't need to do this.x.f.bind(this.x.f)(), only when the function is being separated from it's parent object.

OK: this.x.f()
NOT OK: funcWithCallback(this.x.f)
NOT OK: let callf = this.x.f

[Sjors]

I should just migrate to ES6, so I don't have to think about this :-)