Document deprecation of Marionette.Deferred for #1982

Unless additional configuration is added in v3, this file can be
removed.
Merge pull request #1990 from cmaher/1982-deprecate-deferred

Document deprecation of Marionette.Deferred for #1982
Optimize view.triggerMethod
Add Marionette.deprecate
Merge pull request #1820 from thejameskyle/deprecate

Add Marionette.deprecate
Adds deprecation notice about Application channel.
added childView as getChildViewContainer parameter and updated the private _insertAfter function to pass it through #1983
Add deprecation warning for App regions.