Feature: support PropertyProxies

[tbosch]

In templating, we want to intercept reads/writes to a node. However, adding getters/setters for all properties of node to a proxy object is too slow (we did jsperf tests for this). Solution: introduce PropertyProxies.

A PropertyProxy is an object with the following methods:

• createProxyGet(propertyName): returns a function that gets no arguments and returns the current value
• createProxySet(propertyName): returns a function that gets the new value and applies it.

Integrated into watchtower.js, at every places where a getter is allowed a PropertyProxy should be usable as well.

[tbosch]

Hello Caitlin, I think we don't need this feature any more, after a long discussion with Miško...