Update AlertNode so that configuring alert handlers can be correctly scoped, and easily added.

[nathanielc]

Currently Alert handlers are configured directly on the AlertNode and it is one large flat scope. It would be nice if each alert where configured in its own scope so that you do not have to worry about name conflicts etc.

Goals:

• Make defining multiple Alert handlers in TICKscript easy and intuitive.
• Make writing a new alert handler a simple and isolated task.
• Be able to support(from a code organization perspective) at least dozens of different handlers with ease. The performance profile of multiple handler should already be linear.