Extend social media links for dribble and xing

Extension of the social media in website setting to have a more media possibilities.

***Impacted versions:***

 - Version 8.0


***Current behavior:***

 - In website Settings --> only Twitter, Facebook, Github, Linkedin, Youtube and Google+ are shown  

***Expected behavior:***

 - In website Settings --> there is also the possibility to add Xing and Dribbble account