Reference cycle in Listings VC/VM

[ashfurrow]

Someone raised an excellent point on Twitter that the listings VC that creates the VM creates a subtle reference cycle while referring the VC's functions for presenting modals. Importantly, force-unwrapping self won't work. He also recommends a fix that looks super-nice.

This isn't a big deal, since there's only one instance of each class, and they last the entire lifetime of the app, but in most code this isn't the case, so we should fix it and then write about or at least update the blog post.

[ashfurrow]

I summed up my thoughts on a solution to this issue yesterday: http://stackoverflow.com/questions/31140451/reactivecocoa-retain-cycle-when-passing-closure-as-parameter/34159122#34159122