feat($compile/ngBind): don't add binding info if not enabled

The compiler and ngBind directives add binding information (`ng-binding`
CSS class and `$binding` data object) to elements when they are bound to
the scope. This is only to aid testing and debugging for tools such as
Protractor and Batarang. In production this is unneccesary and add a
performance penalty.

This change disables adding this binding information by default. You can
enable it by calling `$compilerProvider.enableBindingInfo()` in a module
`config()` block.

BREAKING CHANGE:

The `ng-binding` CSS class and the `$binding` data object are no longer
attached to DOM elements that have a binding to the scope, by default.
If you relied on this feature then you can re-enable it in one of your
application modules:

```
someModule.config(['$compileProvider', function($compileProvider) {
  $compileProvider.enableBindingInfo();
}]);
```
Actually we need to pass this `interpolationFn` to the `addBindingInfo` since we need the binding expressions. We can extract them from the `interpolationFn` in `addBindingInfo` so that the whole function is not stored.

It might be possible (with a flag param?) to move the call to `$interpolate` into `addBindingInfo` so that it is not called unncessarily.