Keyboard shortcut for submitting comments

From #1546 

* Use ctrl+enter or cmd+enter to submit comments
* Added `isCommandKey(keyEvent)` method to RESUtils for developing other command key shortcuts

`commandDown` flag is used because otherwise we would need to rely on `e.metaKey`, which may or may not be the command key in all cases. 

Works in comments and the Wiki editor. Could probably be extended to posts if that is desired. 
Ah, I'm setup to use spaces and it appears the rest of the file is in tabs. That might be why. I'll fix it up. I'll also move it below keyboardShortcuts.