feat(mixit15): Go for 2015 !

- Created 2015 event,
- home page cleanup,
- hide menus (sessions, planning, members, speakers,... all pointing on CURRENT event),
- added info menu for 2014,
- updated sponsors documents links
well, they won't be displayed twice but both links are the same. I did'nt want to make a new dev for that, it will be updated (when adding enought 2015 speakers) by the time the users will need it (feb - march).