Add namespaces to AST in the token handler

This decorates the AST with namespace and HTML integration point flags. This will allow us to emit opcodes that can be compiled into a series of DOMHelper (as in #50) objects that swap in and out appropriately for a template's fragments and hydration.
No, it can be any node that has children, namely ProgramNode or ElementNode. It should probably renamed to something more generic like `this.parentStack` and `this.currentParent()`.