Now that #1169 is fixed, the only thing this is used for is to determine whether `onTouchTap` causes touch listeners to be added. The only internal uses of TapEventPlugin are where touch events are already initialized (so this doesn't make a difference) and we don't support `onTouchTap` as part of the public API so this should be safe.
KeyboardEvent now normalizes "charCode", "keyCode", "which" across all browsers
KeyboardEvent has partial "key"-support for KeyDown/KeyUp and full "key"-support for KeyPress.
KeyboardEvent, MouseEvent and TouchEvent now has "getModifierState", polyfill when not implemented.