Store tabText in atom.

This is a combination of tabsOrSpaces and tabSize. I imagine things like these will be stored in a settings object on `atom` at some point.

src/atom/app.coffee

@@ -6,14 +6,16 @@ module.exports =
 class App
   keymap: null
   windows: null
+  tabText: null
 
   constructor: (@loadPath, nativeMethods)->
     @windows = []
     @setupKeymap()
+    @tabText = "  "
 
   setupKeymap: ->
     @keymap = new GlobalKeymap()
-    
+
     $(document).on 'keydown', (e) => @keymap.handleKeyEvent(e)
 
   open: (url) ->