[WebService] Add general notification HTTP endpoint for use by external client.

Since we don't have access to fancy stuff like SignalR or WebSockets, the implementation is based on a simple and dumb long-polling strategy which is absolutely non-scale but should fit our need of ~1.5 people using it simultaneously.
[WebService] Lazy init Build so that the DB is only hit when necessary and don't create a new list if no-one is listening.
Merge pull request #4 from garuma/master

Add general notification HTTP endpoint for use by external client