Computed, Proxy, and Observer properties are not removed if the the model property is reset

[uselessinfo]

Calling the following code will result in a potential memory leak, and may cause some weird issues.

var otherModel = new OtherModel();
masseuseModel.set('foo', masseuse.ProxyProperty('bar', otherModel);

// Do some work
...

otherModel = new OtherModel();
masseuseModel.set('foo', masseuse.ProxyProperty('bar', otherModel);

We need to keep a dictionary of computed, observer, and proxy properties, and perform cleanup of listeners prior to setting the property to something else.

[pajtai]

This might make it worthwhile to turn computed properties to using listeners - as you had it previously - instead of hard coded callbacks, since that way cleaning up Proxies and Computeds could be done in the same way.