Create Blacklist module

[kainsavage]

Currently, the blacklist is just a json blob kept in sync storage. In order to fulfill #21 (which is not scheduled as a part of v2.1.0), the blacklist will need to be changed into a module with read/write functions that abstracts how it is stored.

This interim work can be just creating a single implementation that is a pass-through to sync storage, but paves the way for different implementations in future builds.