Add defaults support in Application.addRegions()

Hi,

Small change - I noticed that the ``defaults`` parameter accepted by ``RegionManager.addRegions(regions, defaults)`` wasn't accepted by ``Application.addRegions(regions)``.  I'm guessing this is because defaults were added to regions fairly recently and the application proxy method was forgotten about at the time of the change.

Without this fix, when setting up an app's regions, either the region definitions have to be written out in full, or you have to hackishly bypass the incomplete method:

``` js
var MyApp = new Backbone.Marionette.Application();
MyApp._regionManager.addRegions({ ... });
```