This commit adds an implementation of a silence storage that can
share store and modify silences, share state via a mesh network,
write and load snapshots, and be dynamically queried.
All data formats are based on protocol buffers.
This adds a new nflog package meant to replace provider.Notifies. It
has a central protobuf type package, which is also meant for usage for
other packages and the API.
The generated Go types are also the in-memory representation.
