Use xing_api gem to load the xing user profile

[johanness]

what changed

• use xing_api gem to facilitate loading xing profile
• add rspec test suite and test touched code
• save oauth token on the user model
• add a profile_loaded field to the user model, to track which users have up-to-date data
• remove unused /test directory
• add config for travis ci

  comments

• travis ci is currently testing fork. TODO update README.md
• profile_loaded field is not used to filter out outdated profiles yet

[birtona]

Thank you very much for your contribution! I have one question: can I just change the travis ci link in the readme and then it tests this project or do I have to register it at travis first?

[birtona]

FYI: I deployed the new version with your changes to Heroku!

[birtona]

forget my question regarding travis, I already figuerd it out, registerd my github account and the project and changed the link in the read me.