Fixed – Menus no longer respond to keyboard navigation

When a menu is active, menu selection should change as characters are typed.
This can be seen in the manual CPMenuTest.

It used to work in the past but with all of the changes in the last few months to the compiler I
was not able to track down the exact commit that broke it. The code responsible for
clearing the _keybuffer after a brief delay in typing, was not being called,
resulting in a build up of characters.

This commit moves the check for delay to the interpretKeyEvent and takes care of
clearing the _keybuffer itself and removes that responsibility from the selection method.
Merge branch 'menuKeyboardNavigationFix' of https://github.com/BlairDuncan/cappuccino into pr-1894