[ALOY-491] Alloy bind() function for creating data binding in code

The only way to create data binding at this point is in markup. It would be nice to be able to create this binding in code as well. I'll have to do some thinking, research, and solicitation of feedback, but it might look something like this:

Alloy.bind($.someLabel, 'text', Alloy.Models.someModel, 'modelProperty');

It should be a function on the Alloy namespace somewhere, not on the proxies to avoid the overhead of adding functions to proxy objects.