expose all remaining key event public api to iOS except translateNativeKeyCode, since iOS has no public sense of key codes
use ASCI table for key code on iOS
moved hidden keyboard to view controller. added will show/hide signals
add initial KeyboardOptions
removed cached mKeyboardString, rely on text field as only copy
pass Window::Format by const&
added iosKeyboard sample
allow for keyboard option updates while visible. simplify keyboard impl by talking directly to the window.
KEY_RETURN returns char '\r', which is consistent with desktop.  other cleanup
expose keyboard textfield and cleanup sample.