[TIMOB-18848] Create a cross-platform API for ActionBar/Toolbar/CommandBar/AppBar

We have no concept of a cross-platform APi for a fairly common UI pattern of an App/Tool/ActionBar. We have Ti.UI.iOS.Toolbar, Ti.Android.ActionBar - and we're looking at exposing Windows' CommandBar and/or AppBar. They are fairly similar and typically involve a bar across the top or bottom of the app with some buttons/navigation. iOS Toolbar: https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/Bars.html#//apple_ref/doc/uid/TP40006556-CH12-SW4 Android ActionBar: http://developer.android.com/guide/topics/ui/actionbar.html Windows CommandBar: https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.controls.commandbar.Aspx Windows AppBar: https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.controls.appbar.Aspx