fix .gitignore for osx
[yanan] add mixpanel offline files for use
Merge remote-tracking branch 'upstream/master'
new exercise
track v1
[yanan] mixpanel offline
Merge remote-tracking branch 'upstream/master'
1.直接通过lesson app的url进入lesson app
2.fix bug:选择题做错了还能重做的bug
add some mixpanel js
hypervideo
Merge pull request #2 from longchao/master

[longchao] flat-ui added
Merge remote-tracking branch 'origin'
[yanan] for merge
Merge remote-tracking branch 'upstream/master'
[longchao] for merge
[yanan] finish the javascript logic of offline-mixpanel and add them to webapp exercise and login
[yanan] minor change to mock_mixpanel_api
[yanan] add webapp testOfflineMixpanel
[yanan] modify the manifest.json file of testOfflineMixpanel
[yanan] minor changes to mixpanel_origin.js