added regionManager.getAll method to retrieve all regions

the motivation: i need a sledge hammer for my current app, and all i had was a tack hammer.

the gist of it is that i want to retrieve all the regions from my application object, so I can pass them in to modules at startup time. it's not an "elegant" solution at this point, but it serves my needs and I can see the value of this as Marionette moves forward with module systems like browserify, requirejs, etc.

the code inside of `RegionManager#getAll` does a `_.clone` of the internal regions object so that changes made by external code won't affect the regionmanager.