Configurable dirty-checking behavior

*Note: this issue originated in https://github.com/aurelia/framework/issues/386- read the comments there first*

Enable developers to decide what Aurelia should do when observing a property will require dirty-checking.

Questions/considerations:

* What is the API for configuring the dirty-checking behavior? Consider https://github.com/aurelia/binding/issues/30 when thinking about the config API.
* What behaviors/options do we ship? log/throw
* PR requires documentation and tests.
* Breaking changes must be avoided.
* Related issue: https://github.com/aurelia/binding/issues/562