Add app.setPath and app.getPath APIs

They can be used to set/get any path defined in PathService

atom/browser/api/lib/app.coffee

@@ -8,6 +8,12 @@ app.__proto__ = EventEmitter.prototype
 app.getHomeDir = ->
   process.env[if process.platform is 'win32' then 'USERPROFILE' else 'HOME']
 
+app.getDataPath = ->
+  app.getPath 'userData'
+
+app.setDataPath = (path) ->
+  app.setPath 'userData', path
+
 app.setApplicationMenu = (menu) ->
   require('menu').setApplicationMenu menu