adds StatusBar extension and demo

I copied the statusbar module from the kitchen sink demo into the extensions. Then I replaced the inline styling with a single rule "display: inline-block". I then created a demo page showing how to use the statusbar and add some static text.

Users should be able to control the look and feel of items they wish to add to the statusbar through css. The only thing they can't do is hide the line / column indicator. For that we would need to augment the extension to accept some option to change the css property on the line / column indicator to "display: none;" but that would be silly at this point because the line / column indicator is all the statusbar extension currently provides.

The documentation mentions something about integrating gcli with ace but I don't see any extension for it or documentation on how to do it. I'm not all that interested in doing it myself unless it's really easy because, I'll probably never use it. For completeness sake though, we should get some kind of extension going to add the commandline if we're going to keep flaunting it in the kitchen sink demo. ;) I'm curious if it would be as easy as dropping the gcli command line into this here statusbar and pointing it at `editor.commands` . . . :D I bet not but, that would be cool.