Add support for Undo, Redo, Cut, Copy, Paste, and Select All from native menus

**NOTE: This pull request should NOT be merged until the native menu request in merged in Brackets. If you run this code with the current brackets master branch, all edit commands will be non-functional.**

These edit commands are handled differently than other menu items.

First, they are sent to the JavaScript code. If the JavaScript code does not handle the command, the shell calls the browser versions of these commands. This way, commands like Undo can be overridden by CodeMirror when an editor has focus, but fall through to the default implementation when a text field has focus.

This pull request also fixes menu redrawing after changing the menu name.