Fix rotation keys [, ], and \ on OS X.

Previously the handlers for these keys had been moved from OnKeyDown to OnKeyChar, apparently for better compatibility with some non-english keyboards.
However this broke the shortcuts on OS X since the event.Skip() call was commented out for OS X.
Rather than uncomment it, I have re-enabled the handlers in OnKeyChar for OS X only. This works better, since on OS X pressing Alt changes the character produced by the keys, so the alt+] etc shortcuts wouldn't work with OnKeyChar. With OnKeyDown they work fine.
Correct direction of ctrl+arrow keys for moving up and down the chart stack
Work around incorrect shortcut text in Windows due to wx2.8 bug
Merge pull request #188 from CaesarSchinas/keyboard

Keyboard shortcut fixes