Add unloadView support. This support includes support for config options on a view to  alwaysAutoUnload:(the view will be unloaded after afterDeactivate every time the view is shown), neverAutoUnload(the view will never be unloaded automatically, no matter how many views are loaded), and use an autoUnloadCount(is set to a number which is used to determine how many views per constraint to leave loaded when transitioning). Fixes issue #3