fix issue that app will crash when we console.log(null)

App will crash when we pass ```null``` as the first parameter to ```console.log()```

You may also notice that ```console.log()``` is different from ```Ti.API.log()```

This PR also enhances Log to accept more than one message, as [Titanium docs](http://docs.appcelerator.com/titanium/latest/#!/api/Global.console-method-log) says:

> The message to log can either be a single argument, or any number of arguments, which will be converted to strings and then concatenated together with a space character.